A reinforcing bar locking device that can be easily locked at a position relatively far from an end portion of a reinforcing bar and apply a strong locking force to the reinforcing bar. The reinforcing bar (10) has a body member (11) having a through hole (11a) in which the reinforcing bar is insertable and also has a pair of fitting members (12) fitted between the reinforcing bar inserted into the through hole (11a) and the inner peripheral surface of the through hole (11a). The inner peripheral surface (11b) of the through hole (11a) is of a funnel shape whose diameter is reduced in the direction of the center axis (C). A female screw thread part (12a) with which the reinforcing bar engages is formed on the inner peripheral surface of the fitting member (12). The outer peripheral surface (12b) of the fitting member (12) is a conical surface that has surface contact with the inner peripheral surface (11b) of the body member (11). On the outer periphery of the body member (11), a substantially cylindrical inserting section (11c) and a flange section (11d) having a larger diameter than the inserting section (11c) are provided. Each of the fitting members (12) has a slit (12c) opened in the direction of the center axis (C) of the through hole (11a).