In the direct-acting valve of the present invention, no flange is formed in the valve box and the piping is achieved by interposing the valve box between pipe flanges. The direct acting valve includes: a driving section that operates by sensing a primary pressure or a secondary pressure; and a valve body communicating with the driving section to open and close a flow path. A valve box of the valve is positioned between pipe flanges tightened by bolts and nuts. Connecting end portions to be mated with pipe flanges respectively have an inlet and an outlet of the flow path, and each of the end portions is formed to have a smaller diameter than that of the pipe flange. A cover flange neck is extended upward from the valve box is formed so as to be interposed between the bolts B and B1 which are provided between the pipe flanges and adjacent to each other on the circumference of the pipe flanges.