In pressure switch type SPL-550, 650 in the pressure carrying section of air or liquids such as water oil, bellows are used to transfer the displacement of the bellows to the actuating lever. The On/Off of quick action type switch is achieved reliably and quickly by means of quick action mechanism which is actuated by the stress of a coil spring installed at the top of the lever. The actuating lever does not stop between the low limit and the upper limit of its travel. It dose not produce error in movement in response to drastic rise or drop in pressure because the actuating lever move rapidly. This pressure switch, which has a narrow pressure gap for adjustment compared with other types, is a highly accurate and reliable pressure control device.