PURPOSE: To provide a machine screw holding fastening structure effective in preventing fastening bolts or screws from being lost in an equipment having the high frequency of parts exchanging on the user side, particularly, effective in preventing the machine screw for a miniature precision equipment such as a wristwatch from being lost.

CONSTITUTION: When an attaching member such as a back cover 11 is fastened to a case body 1 (equipment main body) with a machine screw 40, a washer 50 through which the machine screw 40 is inserted is arranged between the case body 1 and the back cover 11, and the washer 50 is prevented from being follow-turned by the screw-rotation of the machine screw 40 in fastening, and the machine screw 40 and the washer 50 are locked on the back cover 11 after once fastening and integrally removed from the case body 1.