In an electric-motor-assisted bicycle, a motor includes a motor output shaft including a helical gear provided thereon. A reduction gear includes a rotatable shaft and a cylindrical portion. The rotatable shaft extends through the cylindrical portion. A helical gear provided on the cylindrical portion engages the helical gear on the motor output shaft. The rotatable shaft includes a first large-diameter portion, a small-diameter portion and a second large-diameter portion. The reduction gear further includes a bush bearing between an end surface of the first large-diameter portion and an end surface of the second large-diameter portion in the axial direction of the rotatable shaft. The outer periphery of the bush bearing is fixed to the cylindrical portion. The inner periphery of the bush bearing slides in a circumferential direction relative to the small-diameter portion. The bush bearing moves in the axial direction.