Oil pan structure for internal combustion engine

An oil pan structure for an internal combustion engine, the oil pan structure comprising a storing portion that stores oil for an internal combustion engine, wherein the storing portion includes a shallow bottom portion, a deep bottom portion having a larger depth than a depth of the shallow bottom portion, and a connection surface that connects the shallow bottom portion and the deep bottom portion between the shallow bottom portion and the deep bottom portion, wherein the shallow bottom portion and the deep bottom portion are arranged adjacent to each other along a longitudinal direction of the oil pan structure, wherein the oil pan structure comprises a side wall disposed at an opposite side of the shallow bottom portion from the connection surface, a first rib is disposed on a back surface of the shallow bottom portion so as to extend from one side of the side wall in a width direction of the shallow bottom portion toward an end portion of the connection surface on an opposite side in the width direction which is opposite to the one side, wherein the width direction of the shallow bottom portion is perpendicular to the longitudinal direction of the oil pan structure wherein the first rib extends diagonally with respect to longitudinal direction of the oil pan structure, and wherein the first rib connects a portion of the side wall located on the one side of the side wall in the width direction and the end portion of the connection surface located on the opposite side of the connection surface in the width direction.