A piston cooling structure for a multicylinder engine having oil jets for ejecting oil toward pistons. The oil jets are mounted in each of a plurality of journal walls except one journal wall. The piston cooling structure is able to supply oil to a cylinder head in a position closer to a central region along the axis of the crankshaft while avoiding a complex oil passage shape. An oil passage for guiding oil to a cylinder head is defined in the one of the journal walls without an oil jet, and this one journal wall is disposed between a pair of adjacent cylinder bores. Oil jets are mounted in each of the other journal walls. A crankshaft of the engine is rotatably supported by the journal walls.