To provide a fastening means to be used even at a limited space and besides increase a locking effect.

A part of a screw hole 3 joined in a screwed in state with the screw thread 2a of a screw shaft is fitted in a taper recessed part 4 notched obliquely of an axis toward the center of the screw hole 3. In a state before fastening of the screw shaft, a protrusion part protruding to the seat surface side is formed and insertable in a taper recessed part 4 along with press to the protrusion part, and a locking member 1 provided with a screw thread 1a continued to a screw thread 3a of a screw hole 3 is arranged. The protrusion part on which fastening from the seat side is exerted is axially pressed, and the locking member 1 is advanced in the taper recessed part 4. As a result of bearing from a taper surface being applied and a stress in an orthogonal direction to an axis being exerted on the screw thread 1a of the locking member 1, the fastening force of a screw is increased, whereby a using screw shaft is shortened and a sufficient fastening force is ensured.