Rotation position detection device for change drum and motorcycle

The purpose of the present invention is to be capable of suppressing, as far as possible, rotation position detection errors and to be capable of minimizing, as far as possible, restrictions on layout when attaching a rotation position detection device to, e.g., a case, said rotation position detection device detecting the rotation position of a change drum. The rotation position detection device comprises a change drum, a magnetic field generation unit, and a magnetic field detection unit. The magnetic field detection unit is fixed to the change drum and rotates in conjunction with the change drum, thereby changing surrounding magnetic fields. The magnetic field detection unit is formed separately from the magnetic field generation unit, is fixed at a position at which the magnetic field changes in accordance with the rotation of the magnetic field generation unit, detects magnetic fields, and, on the basis of the detection results, outputs a signal corresponding to the rotation position of the change drum.