PURPOSE: To securely prevent slide portions between a valve guide and a valve stem from causing deposition even in the case of sludge component flowing into combustion gas by suppling lubricating oil to the slide portions.

CONSTITUTION: On the way of a gas pipe 18 for supplying gas fuel to a sub- chamber 10 is interposed a check valve 24. Then, a lubricating oil pipe 40 is disposed coaxially in the gas pipe 18. Also, to the upper end of a valve guide 33 in the check valve 24 is secured fixedly a lubricating oil receiver 50 having the upper end opened to surround a valve stem 34, and lubricating oil supplied from said pipe 40 is stored in an oil chamber 51 in the receiver 50. And to a slide portion 53 between the valve guide 33 and the valve stem 34 is supplied lubricating oil in the oil chamber 51 as the valve stem 34 moves vertically, i.e., the check valve 24 is opened and closed. Thus, the slide portion 53 is prevented from deposition even when sludge components flow into combustion gas.