To provide a transmission capable of securing oil quantity recovered to an oil pan even in a case where the volume of an oil pan cannot be sufficiently large.

This transmission is provided with a first member 31 having a cylindrical part, and an internal spline 35 on an inner circumference of the cylindrical part, that is integrally rotated with an input shaft 10, and a second member 41, having a cylindrical part, and an external spline 44 in an outer circumference of the cylindrical part to be engaged with the internal spline. The external spline 44 of the second member 41 has a recess 42 formed partly or wholly in its groove. When it is engaged with the internal spline 35 of the first member 31, a cavity 43 is formed of the recess 42 from an inner part surrounded by the first member 31 and the second member 41 through outward.