A piston-returning apparatus for a disc brake includes two pushing plates, a collar, a rotating unit and a handle. Each of the pushing plates includes a threaded element. The collar includes two screw holes for receiving the threaded elements of the pushing plates respectively so that the pushing plates are synchronously moved toward or away from the collar when the collar is rotated. The handle is connected to the collar via the rotating unit. The rotating unit is switchable between two modes. In the first mode, the rotating unit rotates the collar clockwise when the handle is pivoted clockwise but the rotating unit does not rotate the collar counterclockwise when the handle is pivoted counterclockwise. In the second mode, the rotating unit rotates the collar counterclockwise when the handle is pivoted counterclockwise but the rotating unit does not rotate the collar clockwise when the handle is pivoted clockwise.