To prevent liquid from entering a container from between an operation knob and a cylinder, even if being splattered with the liquid such as water.

A switch device includes: a container 10 for storing a contact; a rectangular frame-shaped cylinder 2 provided on an upper part of the container; an operation knob 1 blocking an opening 2a at an upper end of the cylinder 2, rockably supported on the cylinder by a shaft 2j, and opening/closing the contact by rocking operation; and a plunger 3 provided on one side wall 2f side of side walls 2f and 2b of the cylinder 2 vertical to a rocking surface of the operation knob 1, over the lateral width of the side wall 2f. The plunger 3 projects out from the side wall 2f of the cylinder 2, and linearly and elastically contact with the side wall 2f and a side wall 1f of the operation knob 1 opposing to the side wall 2f over the lateral width of the side wall 1f. The projecting direction of the plunger 3 inclines to the side wall 2f of the cylinder 2.