A power-and-free conveyor comprising a carrier including front, rear and intermediate free trolleys at least three in number, a first connecting bar supported by the intermediate free trolley and either one of the front and rear free trolleys, a rail provided on the first connecting bar and extending along the conveyor line, at least two roller trap portions formed in the rail and spaced apart by a predetermined distance longitudinally of the rail, a second connecting bar supported by the first connecting bar and the other of the front and rear free trolleys, and a roller supported by the second connecting bar as projected thereabove and rollingly movable along the rail; and a roller releasing device for releasing the roller from the trap portion and returning the roller onto the rail. For the transport of an article, the roller is caused to fall into the trap portion of the rail most proximate to the second connecting bar. When the carrier is to be retained in a standby position at an accumulation section, the roller is caused to fall into the trap portion of the rail remotest from the second connecting bar.