To provide an operating knob of a key cylinder capable of being easily removed.

In the operating knob 7 of the key cylinder 3 fixed to the end section of a cylinder inner 6 having a key insertion hole 11, the operating knob 7 includes a key insertion port 22 for inserting a key 9 formed in the operating knob 7 so as to be connected to the key insertion hole 11 of the cylinder inner 6 and an engagement receiving section 27 engaged with an engagement section 14 formed in the end section of the cylinder inner 6, and a projection 28 moving the engagement receiving section 27 in the direction of engagement release by inserting a key 9 in the key insertion port 22 is provided on an insertion course of the key 9.