To provide an air valve fastening tool for use in fastening a fixed nut of an out set type air valve attached to a vehicle wheel, which easily fastens the fixed nut with a predetermined fastening torque without removing a tire.

An air valve fastening tool includes: a cylindrical socket 1 having a circular wrench 11 formed in an inner peripheral section of a top end and fixed to a fixed nut 7 of an air valve 6, and a nut section 12 provided in an outer circumferential section of a base end for hooking a torque wrench 3; a driver-like presser 2 having a coupler 22 provided at the top end and screwed in a valve cap attaching screw 61 at a tip of a stem 60 of the air valve 6, and which is inserted into the socket from a base end side of the socket 1. The socket 1 is mounted on the fixed nut 7. The coupler 22 is screwed into the valve cap attaching screw 61 by inserting the presser 2 into the socket 1, to rotate the socket 1 by the torque wrench 3.