PURPOSE: To provide a cylinder head cooling mechanism of an engine to make flow adjustment of cooling water desirable in accordance with the drive state of the engine.

CONSTITUTION: It is presumed that an engine is an auxiliary chamber type diesel engine furnished with an auxiliary combustion chamber 3 on one side in the cross direction of a cylinder head 1 and an exhaust port 4 on the other side in the cross direction of the cylinder head 1. Under this presumption, a cooling water inlet 6 is provided on one end side in the cylinder arrangement direction on the cylinder head 1, while a first cooling water outlet 9 is provided on one side in the cross direction of the cylinder head 1 on the other end side in the cylinder arrangement direction of the cylinder head 1. Additionally, by providing a second cooling water outlet 9 on the other side in the cross direction of the cylinder head 1, it is devised to heighten ignitability by way of making the flow of cooling water inside of the cylinder head 1 sided to the other side in the cross direction of the cylinder head 1 by flowing cooling water out only from the second cooling water outlet 9 at the time when temperature of cooling water is low by a thermostat valve 13.