A switch device includes a base board having a face on which a fixed contact is provided and an elastic sheet that covers the face of the base board. The elastic sheet includes a contact dome part that covers the fixed contact to form a contact chamber, a movable contact that is provided on the contact dome part, a first recessed part that forms an air accumulating chamber, a second recessed part that forms a foreign material accumulating chamber, a guide groove that has a straight part and a circular arc part to form a guide passage for communicating the air accumulating chamber with the foreign material accumulating chamber, a nonreturn part provided inside the circular arc part, and a vent groove connected to the contact dome part and the guide groove to form a vent passage for communicating the contact chamber with the guide passage.