A baffle plate 17 inside an oil pan 16 attached to the lower part of an engine cylinder block is spherically shaped so as to bulge upward, and oil dropping holes are formed in low positions in this baffle plate 17. Return oil flow from the engine lubricating operation drops from the engine onto the baffle plate and travels along the baffle plate toward the walls of the oil pan, this travel facilitating removal of air which became mixed with the oil during the lubricating operation. Oil dropping holes are formed in low positions in the baffle plate to communicate the oil return to the pool of same in the oil pan. In addition, beads 19 that direct oil flow toward the oil dropping holes are provided on baffle plate 17. In addition to eliminating poor engine lubrication operation due to air entrapped in the lubricating oil by helping rid the oil of the air, the spherically shaped baffle plate has enhanced resistance to cracking under loading imposed thereon.