To provide an easily manufacturable oil pan and its manufacturing method having ribs partitioning an oil pan body interior and holes communicating each partitioned parts partitioned by the ribs.

In the oil pan 11, the ribs 13 partitioning the interior in longitudinal and width directions are provided in the interior of an oil pan body 12 provided in a lower part of an internal combustion engine, and the oil circulating holes 15 are formed in bottoms of crossing portions 14 of the ribs 13. In the manufacturing method of the oil pan 11, when forming the oil pan 11 by casting, the ribs 13 partitioning the interior in the longitudinal and width directions are integrally formed by casting in the interior of the oil pan body 12, and the oil circulating holes 15 are formed by casting on the bottoms of the crossing portions 14 of the ribs I3.