A starter mounting structure for a starter for cranking an engine (1) has a transmission case (2a) surrounding the transmission (2) and having an engine side end surface (200) facing an engine side. The engine block (1b) has a transmission side end surface (110, 120) facing a transmission side and partially overlapping the engine side end surface (200) of the transmission case (2a). An outer periphery (140) of the transmission side end surface (110, 120) of the engine block is partially equipped with a recess which extends on a crankshaft (5) side with respect to an inner periphery (240) of the engine side end surface (200) of the transmission case. An opening portion (13) is formed in correspondence with the recess. The starter mounting structure has a starter mounting member (9) closing the opening portion (13) and supporting the starter (8).