A mounting structure for mounting a separate shaft type oil pump in a case of a transmission. The separate shaft type oil pump is driven by a shaft that is separate from and rotated in cooperation with a shaft arranged in a torque input route extending from an engine to the transmission to supply hydraulic oil to a transmission oil pressure control mechanism. The mounting structure includes a spacer coupler that fastens the oil pump to the transmission case. The spacer coupler includes a plurality of spacers that couple the oil pump and the transmission case. An oil passage is formed in the spacers of the spacer coupler to connect an oil pressure system, which includes the oil pressure control mechanism, and the oil pump. A manual shaft for operating the transmission is arranged in a clearance between the spacers of the spacer coupler.