A holding structure of a tire air pressure detecting device, comprising: a wheel in which a tire is mounted on a wheel rim ; a tire valve which is fixed to the wheel rim ; a tire air pressure detecting device which is held by a screw shaft protruding on an inner side of the tire in the tire valve ; a fixing nut which is screwed to the screw shaft and configured to fix the tire valve to the wheel rim ; a holding sleeve which is screwed to the screw shaft and configured to hold the tire air pressure detecting device on the screw shaft ; and an elastic member which is sandwiched between the tire air pressure detecting device and a device supporting portion including at least one of the fixing nut , the holding sleeve and the wheel rim in an axial direction of the screw shaft , wherein: the tire air pressure detecting device is in a floating support state capable of being elastically displaced toward the fixing nut side in the axial direction of the screw shaft , the tire air pressure detecting device comprises a case side rotation restricting portion which engages with the elastic member in a case which accommodates equipment, and the elastic member comprises a rotation restricting portion which is configured to restrict rotation of the tire air pressure detecting device around the screw shaft by engaging with the case side rotation restricting portion , characterized in that the elastic member is integrally mounted on the fixing nut . a wheel in which a tire is mounted on a wheel rim ; a tire valve which is fixed to the wheel rim ; a tire air pressure detecting device which is held by a screw shaft protruding on an inner side of the tire in the tire valve ; a fixing nut which is screwed to the screw shaft and configured to fix the tire valve to the wheel rim ; a holding sleeve which is screwed to the screw shaft and configured to hold the tire air pressure detecting device on the screw shaft ; and an elastic member which is sandwiched between the tire air pressure detecting device and a device supporting portion including at least one of the fixing nut , the holding sleeve and the wheel rim in an axial direction of the screw shaft , wherein: the tire air pressure detecting device is in a floating support state capable of being elastically displaced toward the fixing nut side in the axial direction of the screw shaft , the tire air pressure detecting device comprises a case side rotation restricting portion which engages with the elastic member in a case which accommodates equipment, and the elastic member comprises a rotation restricting portion which is configured to restrict rotation of the tire air pressure detecting device around the screw shaft by engaging with the case side rotation restricting portion , characterized in that the elastic member is integrally mounted on the fixing nut . the tire air pressure detecting device is in a floating support state capable of being elastically displaced toward the fixing nut side in the axial direction of the screw shaft , the tire air pressure detecting device comprises a case side rotation restricting portion which engages with the elastic member in a case which accommodates equipment, and the elastic member comprises a rotation restricting portion which is configured to restrict rotation of the tire air pressure detecting device around the screw shaft by engaging with the case side rotation restricting portion , characterized in that the elastic member is integrally mounted on the fixing nut . <EOS>