TRANSMISSION DEVICE

To improve the degree of freedom of assembly, a power transmission device is suggested having a case formed by assembling a first case member and a second case member; and a shaft member supported by the case, the power transmission device comprising: a protrusion provided to the first case member and protruding in the axial direction along to the direction of assembling the case; and a recess provided to the second case member and recessed in the axial direction. The shaft member is supported by the protrusion in the recess.