To provide a locking mechanism of an operating knob, wherein a through hole of a case covering the operating knob can be easily made small to miniaturize the mechanism, and the positions where the operating knob can be locked can be set at one or more desired spots by a locking knob.

This locking mechanism is equipped with a case 80 wherein a through hole 81 is provided, the operating knob 100 wherein a pressing part inserting part 101 is provided, a sliding object 30 to slide by being linked with the operating knob 100 through the case 80, the locking knob 60 formed by providing a pressing part 63 on the upper surface of a base part 61 installed between the case 80 and the sliding object 30, and a springing means 50 to spring the locking knob 60 so that the pressing part 63 is exposed from the pressing part inserting part 101 of the operating knob 100. Engagement releasing parts 83, 85, 67, 69 comprising recessed and projecting parts to lock the movement of the locking knob 60 in its sliding direction and to release the locking by pressing the pressing part 63 of the locking knob 60 is provided on both of the lower surface of the case 80 and the base part 61 of the locking knob 60.