Provided is a switch device with high operation reliability in which an opening-closing contact portion is not erroneously opened or closed even when an external impact is applied. A switch unit, which is configured to be separable from an operation unit, is provided with a rotary drive plate, which rotates between a standby position and a usage position, drives an opening-closing contact mechanism of the switch unit in the standby position to assume an opening-closing state at the time the operation unit is at an operation position, and drives the opening-closing contact mechanism in the usage position to assume an opening-closing state at the time the operation unit is at a standby position. The operation unit is provided with an engagement portion that is engaged with the rotary drive plate when the operation unit is joined and attached to the switch unit and rotary-drives the rotary drive plate from the standby position to the usage position. The opening-closing contact mechanism is set to a predetermined opening-closing state by detaching/attaching the operation unit from/to the switch unit.