To constitute a load detector by the minimum number of parts so as to simplify a structure of a bicycle and reduce cost by providing a torsion bar in a pedal stepping force transmission path and detecting load based on torsion amount (difference in pulse phase) of the torsion bar.

A torsion bar 24 which constitutes a torque detection mechanism 17 is supported on a cylindrical case body 25 fixed by facing to the right and left on a rear frame through a pair of bearings 26 on the right and left, and one end is integrally connected to an axle of a rear wheel on the left side. A rear sprocket for pedal is mounted on the other end through a one-way clutch. A hole IC 29 mounted on both ends on the right and left of the case body 25 is arranged in proximity at a position where multipole polarising rings 28 on the right and left oppose. When the torsion bar 24 rotates, power generation force is generated every time a magnetic field of the multipole polarising rings 28 passes, and a pulse signal which corresponds to the rotation is output due to its repetition. In this way, load is detected based on torsion of the torsion bar 24 provided in a pedal stepping force transmission path.