PURPOSE: To prevent the operatability of a small size electronic apparatus and the appearance of a shoulder hang type musical instrument from being deteriorated.

CONSTITUTION: An installing device 1 consists of a nearly flat surface shaped plate part 11 on which a small size electron musical instrument is placed a fixing part 14 for engaging the installing device 1 with a strap pin 17, and an arm part 16 for connecting the plate part 11 and the fixing part 14 to each other. A fixing tool 12 is provided on the mounting surface of the plate part 11, and a suction cup 13 is provided on the back surface thereof. A strap pin installing hole 15 which is engaged with a strap pin 17 provided on a shoulder hang type musical instrument is provided on the fixing part 14. In the installing device 1, the small size electron apparatus is fixed to the front surface of an electric guitar by utilizing the suction cup 13 and the strap pin 17, so that it is possible to operate the small size electron apparatus easily without injuring and staining the electric guitar.