Steve Carell, the bumbling star of NBC’s “The Office,” plans to leave the series at the end of the next season, potentially dealing a setback to the network as it tries to rejuvenate its prime time schedule.

“The Office” is NBC’s No. 1 prime-time show among the 18- to 49-year-old viewers that advertisers value, in part because of Mr. Carell, who has played the boss of Dunder Mifflin, Michael Scott, since the show’s debut in 2005.

In recent years, it has been a rare bright spot on the schedule of the low-rated network.

In separate interviews last weekend, Mr. Carell seemed to confirm reports that he would leave when his contract expires at the end of the 2010-11 season.

Image Steve Carell has been on ”The Office” on NBC since the show's premiere in 2005. Credit... Byron Cohen/NBC

“I just think it’s time,” Mr. Carell was quoted as saying on E! Online. “I want to fulfill my contract. When I first signed on, I had a contract for seven seasons, and this coming year is my seventh. I just thought it was time for my character to go.” Entertainment Weekly quoted him as making similar remarks.