To provide a technique for restricting leak of oil from coupling surfaces of a cylinder block with an oil pan.

This structure is provided with the cylinder block 5, and the oil pan 1 coupled with the cylinder block 5, and comprising thermoplastic resin at least at coupling positions 2a and 4a to the cylinder block 5. The oil pan 1 is partly fused or softened at the coupling positions 2a and 4a to the cylinder block 5 to be tightly attached to the cylinder block 5. The coupling positions 2a and 4a of the oil pan 1 are fused or softened by ultrasonic waves, for example, to be tightly attached to the cylinder block to secure sealing performance.