A clutch plate is supported by a clutch housing which rotates in unison with an input shaft. Another clutch plate is supported by a clutch hub which rotates in unison with an output shaft. These clutch plates are disposed adjacent each other and are pressed and engaged with each other by a clutch piston through a pressure plate. A hydraulic pump is driven by the pressure plate through a pump driving member fitted to an outer periphery of the output shaft. Lubricating oil supplied from a lubricating oil port is conducted to the clutch plates through a lubricating oil passage formed between an outer periphery of the output shaft and an inner periphery of the pump driving member. The lubricating oil passage for conducting the lubricating oil to frictional engagement elements of the hydraulic clutch is formed outside the rotatable shaft, thereby reducing the fabricating cost of the apparatus.