PURPOSE: A shaft aligning device of a nuclear reactor coolant pump is provided to prevent a vibration and an abrasion in advance by preventing a damage of a fastening member which fastens an impeller and a pump and preventing the shaft center of the impeller and the pump shaft from being warped. CONSTITUTION: A shaft aligning device of a nuclear reactor coolant pump has half-grooves (11a,13a) which are symmetrical with each other in order to form a pair of pin grooves by being merged on a contact surface on which a pump shaft (11) and an impeller (13) come into contact with each other. A fastening hole (18a) is formed by a penetration of an alignment pin (18) in a central part in a radial direction. A fastening hole (11b) is formed so that a fastening screw (19) fastens the alignment pin in the contact surface of the pump shaft through the fastening hole.
