To provide a mounting instrument capable of fixing a device on board with optimal load.

A screw threadably engages a fastening member 30 through an aperture 16 on rear surface 12 of a fixing member 10 and tip of the screw projects through an aperture 15 on front surface 11 of the fixing member 10. A protuberance 34 of the fastening member 30 is fitted in a recessed part 17 of the fixing member 10. The protuberance 34 comes off the recessed part 17 of the fixing member 10 by a protuberance supported part 33 or the protuberance 34 deforming when torque applied on the screw reaches predefined value. Thereby, the fastening member 30 rotates in same direction along with rotation of the screw and the torque applied on the screw does not exceed the predefined value. A contact piece 37 provided on the fastening member 30 comes into contact with a contact protuberant part provided on the fixing member 10 when the fastening member 30 rotates and periodical contact sound is generated.