To provide an operation knob of an engine starting system, which can be applied to a conventional cylinder lock so as to constitute a smart ignition device; and to provide the engine starting system using the operation knob.

The operation knob 8 of the engine staring system is provided with a key plate 80 which is equipped with a key mountain portion for being inserted into a key cylinder lock 3, and a knob portion 81 which is gripped when the key plate 80 is inserted into an insertion hole and turned. The cylinder lock 3 includes: a rotor 30 which is rotatably arranged inside a body portion 20, and in which the insertion hole is formed in such a shape as to be elongated in an axial direction; and a plurality of tumblers 31 which are provided movably in the axial direction of the rotor 30, which are urged to a radial outside so as to be engaged with a tumbler engaging portion 24, and which are disengaged from the body portion 20 by being disengaged from the engaging portion when a normal key is inserted into the insertion hole. The key mounting portion, which is formed on the key plate 80 is formed in such a prescribed shape as to mesh with the tumbler 31 when the key is inserted into the insertion hole.