PURPOSE: To effectively cool lubrication oil with a simple structure.

CONSTITUTION: A passage outlet 4a of a lubrication oil passage 4 is opened at the periphery of a crank pin 3 in a crank shaft 2 of an engine 1. Lubrication oil 6 pressurized by a hydraulic pump 5 is fed under pressure from the lubrication passage 4 to slide parts 7, and is jetted from a jet hole 9 directed to the rear side 8a of a piston 8 which is therefore cooled. An oil communication hole 10c communicating between the outer surface 10b and the inner surface 10 of a crank pin metal 10 is formed in the pin metal 10. Further, the outlet port 9a of the jet hole 9 is formed in the large end part 11 of a connecting rod, and the inlet port 9a thereof is opened at the inner surface part of 11a of the large end part 11 of the connecting rod. An oil introduction passage 4 for communicating between the lubrication oil passage outlet port 4a and the jet hole inlet port 9b through the oil communication hole 10c in the crank pin metal 10 is formed in the inner surface 11a of the large end part 11 of the connecting rod.