A power-assisted bicycle is provided with a one-way clutch that can also be used as a torque detection apparatus. The one-way clutch has a tooth part (112) mounted on a driven means and a piece part (100) mounted slidably yet non-rotatably on a drive shaft (4). The tooth part has a first engagement face (121) formed with a plurality of teeth (114) and the piece part has a second engagement face (110) formed with a plurality of pieces (102). The first engagement face and the second engagement face are disposed facing each other generally perpendicularly to the axial direction. A disc spring (124) is disposed on the rear face of the piece part. As the piece part rotates in the direction of running forward, the piece is engaged with a sharply sloping face of the tooth to engage with the tooth and the angle of the piece with respect to the second engagement face increases, whereby the piece slides so as to increase the distance from the tooth part in resistance to the disc spring. As the piece rotates in the opposite direction, the piece abuts with the gently sloping face of the tooth and the angle of the piece with respect to the second engagement face is made smaller to decrease the distance from the tooth part by means of the elasticity of the disc spring.