A slide valve is provided, in which the conductance in the minimum region is controllable with high accuracy to enable stable control, a slide plate is prevented from plastically deforming to acquire good controllability of the minimum flow rate, and it is possible to detach a valve element and an air drive portion integrally with the slide plate, thereby facilitating the maintenance. The slide valve includes a body having a flow path, a slide plate provided within the body and between a closing position preventing a flow on the flow path and an open position permitting the flow, disposed perpendicularly relative to a flow path axis and movable horizontally or on a straight line, and a valve element incorporated in the slide plate and operated in a direction of the flow path axis to switch between the closing position and the open position of the slide plate by air cylinder drive. The slide plate has an upper surface and a lower surface that form small clearances in cooperation with the body when the valve element is in the open position, thereby enabling control of the minimum conductance. When the valve element has been in the closing position to induce a pressure difference load, the slide plate when receiving the pressure difference load is not plastically deformed.