Moretti's stirring account of a happy family shattered by the death of a teen-age son received the Palme d'Or.
"The Piano Teacher," Austrian director Michael Haneke's dark tale of a sexually repressed music instructor seduced by a student, won the grand prize, the festival's second-highest honor.
Isabelle Huppert and Benoit Magimel, stars of "The Piano Teacher," received the best actress and actor awards.
After accepting the Palme d'Or, Moretti emotionally thanked everyone involved with the film and threw his arms in the air in elation.
"The Son's Room" features a character named Giovanni living a near-perfect life with his wife and two children. Then his teen-age son is killed in a freak diving accident.
Moretti, who plays the lead, intelligently examines how people cope with the worst that can happen to a family.
Take a virtual tour of the Cannes Film Festival.
Huppert was the Cannes jury's unanimous choice for best actress.
"I thank Bach, Schubert and Mozart," said Huppert, who performed some of the film's piano pieces herself.
Best-director honors were split between Joel Coen for his film-noir thriller "ThMan Who Wasn't There," co-written with his brother, Ethan, and David Lynch for his enigmatic Hollywood tale "Mulholland Drive."
The directing awards were presented by Jodie Foster, who had to drop out as Cannes jury president because of a scheduling conflict for a film she was shooting.
|From "La Pianiste," Cannes' best director Michael Haneke, best actress Isabelle Huppert and best actor Benoit Magimel|
The screenplay award went to Bosnia's Danis Tanovic for the irreverent war satire "No Man's Land," which he also directed.
The jury awarded a prize for technical achievements to Tu Duu-Chih, sound designer for two films in competition, "Millennium Mambo" and "What Time Is It There?"
Director and actress Liv Ullmann headed the 10-member Cannes jury, which included directors Terry Gilliam and Edward Yang and actresses Julia Ormond and Charlotte Gainsbourg.
The festival closed Sunday night with French director Raoul Ruiz's period drama "Les Ames Fortes," starring model Laetitia Casta.
The top prize in a separate competition called "Un Certain Regard" went to first-time French director Yves Caumon for "Boyhood Loves." The competition included films that did not make the main awards category, but were deemed worthy of screening at the festival.
"Boyhood Loves" stars Mathieu Amalric as a man trying to reconnect with his neglected parents after his father takes ill.
This year's festival was not a huge hit among film critics or the spectators who gather outside the red-carpet arrivals area for a glimpse of the stars.
Critics generally found the lineup of movies unexciting compared to last year's event, which included Lars von Trier's divisive musical "Dancer in the Dark," winner of the Palme d'Or, and such acclaimed films as Yang's "Yi Yi," Ullmann's "Faithless" and the Coen brothers' "O Brother, Where Art Thou?"
And celebrity watchers complained that top stars were scarce this year. Those who did turn up included Sean Penn, Frances McDormand, Tim Robbins and Jennifer Jason Leigh.
For the closing-night film, spectators were treated to visits by Melanie Griffith, who was honored at Cannes with a lifetime achievement award, and her husband, Antonio Banderas; Milla Jovovich; and Nick Nolte, who is shooting Neil Jordan's film "Double Down" in France.
Nicole Kidman, the star of opening-night film "Moulin Rouge," provided a festivahighlight when she wandered off the red carpet at the movie's premiere to shake hands with fans.
Another highlight was the return of Francis Ford Coppola with "Apocalypse Now Redux," a new version of his Vietnam epic that won the Palme d'Or in 1979. Coppola added 53 minutes of footage cut from the original release, restoring some darkly funny moments and a dreamlike French plantation scene.
"Thirty years later, his masterpiece is there and growing," Ullmann said at the closing ceremony.
By David Germain
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