A check valve, a retainer and a washer are secured to a valve body by inserting a pin therethrough and staking a distal end portion of the pin to form a staked portion. A restraining member is interposed between the washer and the staked portion. The fit clearance between the restraining member and the shank of the pin is set smaller than the fit clearance between the check valve, the retainer and the washer on the one hand and the shank of the pin on the other. Thus, when the distal end portion of the pin is staked, the deformation of the shank of the pin is restrained by the restraining member that defines a small clearance between the same and the pin. Therefore, it is possible to suppress the enlargement in diameter of a portion of the pin where the check valve is fitted and hence possible to prevent deformation of the check valve. Thus, stable valve characteristics can be obtained.