To provide a pressure-resistant component, having high strength against the pressure of an inside fluid, without making the component large in size.

When pressure from an inside fluid acts on the inside of a cylinder part main body 20 and a blocking member 21, a force for moving the blocking member 21 in the direction of the opening of the cylinder part main body 20 is generated, and the force is applied between the inner peripheral surface of a cylinder section 20a of the main body 20 and the outer peripheral part of a contact section 21a of the blocking member 21, while the outer peripheral surface of a blocking section 21b of the blocking member 21 is pressed against the inner peripheral surface of an engaging section 20b of the main body 20. Since the outside diameter of the blocking member 21 is larger than the diameter of the opening of the main body 20 herein, the movement of the blocking member 21 toward the outside of the cylinder part main body 20, when the pressure of the inside fluid rises extremely is held down.