A vehicular automatic transmission including a first planetary gear device and a first set of frictional coupling elements, which can be supported by a pump housing via first and second retainer rings, at predetermined axial positions within the pump housing, during assembling of the automatic transmission. The first retainer ring is fixed to a radially inner spline-fitting part of a cylindrical extending portion of the pump housing, while the second retainer ring is fitted in a first circumferential groove formed in a ring gear of the first planetary gear device and a second circumferential groove formed in the inner circumferential surface of a splined cylindrical portion of a first hub splined to the outer circumferential surface of the ring gear and the radially inner portions of the first set of frictional coupling elements. The automatic transmission is manufactured by assembling a subassembly with respect to a stationary cylindrical housing to which the pump housing is fixed. The subassembly includes the pump housing provided with an oil pump, first planetary gear device and first set of frictional coupling elements.