A pedal-side rotating member is composed of a boss portion rotatably supported by a pedal shaft, a spring holding portion for holding one end of a return spring, a stopper arm being operatively in contact with an inner wall surface of a supporting body, and a mechanically-weaker portion, wherein the boss portion, the spring holding portion, the stopper arm and the mechanically-weaker portion are integrally formed as one unit. The spring holding portion is so configured as to be broken away from the boss portion at the mechanically-weaker portion, if an acting force larger than a predetermined value is applied to the stopper arm when the rotating member is rotated in a direction to an acceleration fully-closed position. A broken piece is held at a position inside of the supporting body, so that rotation of the boss portion is not adversely affected by the broken piece.