To miniaturize the whole clutch by making smaller the inner diameter and the outer diameter of a clutch disk.

An input gear 4 provided with a cylinder shaft 6 surrounding the outer peripheral face of an output shaft is fitted freely rotatably to the output shaft 1. A plurality of the clutch disks 10 fitted to a spline 9 formed on the inner peripheral face of the cylinder shaft 6 and a plurality of the clutch disks 14 fitted to the spline 9 formed on the outer peripheral face of the output shaft 1 are provided in an annular space 7 between facing surfaces of the output shaft 1 and the cylinder shaft 6, so as to be alternately overlapped in the axial direction and so that the clutch disk 10 located on the outermost side is brought into contact with a pressing plate 11 fitted to the inner peripheral face of an opening end part of the cylinder shaft 6. And at the same time, a piston 16 capable of pushing and moving each clutch disk 10, 14 in the axial direction by oil pressure is stored in the annular space 7 between the facing surfaces of the clutch disk 10 located on the innermost side and the input gear 4.