PURPOSE: To reduce any harm caused by blow-by gas, and also reduce the consumption amount of lubricating oil for a long time, stably and surely.

CONSTITUTION: One or a plurality of oil drain hole(s) 9 penetrating from a land surface toward a piston back surface is(are) provided in a range distributed in about 45 degree in right and left direction or more preferably 30 degree from the thrust side center of a piston 1 on a land just above the oil ring groove 4 of the piston 1.