Inspection hole plug

An inspection hole plug that plugs an inspection hole of an outer casing surrounding a tube bundle in a steam generator, the inspection hole plug comprising:

• a base fixed to the outer casing and having an opening that serves as the inspection hole;
• a fitting member that plugs the opening of the base;
• a fitting unit that guides rotational movement of the fitting member in a circumferential direction along an inner peripheral edge of the opening of the base, and restricts the rotational movement by an axial movement of the fitting member parallel to a shaft center of the rotational movement to fit the inner peripheral edge of the opening of the base and an outer peripheral edge of the fitting member to each other;
• a holding member into which a shaft portion extending from the fitting member along the axial direction is inserted and that is provided to be capable of abutting on the base;
• and
• a fastening member that is screwed onto the shaft portion of the fitting member and holds the fitting member at a position axially moved by fastening thereof with the holding member abutting on the base,
• wherein in the steam generator, a bore through which the inspection hole can be seen from outside of a body that covers around the outer casing is formed in the body, and
• the holding member includes a restricting member arranged in the bore in a state with the holding member abutting on the base to restrict passage of the fastening member toward the outer casing between an inner periphery of the bore and the holding member.