To reliably detect liquid leakage even in the case of liquid having extremely poor conductivity, such as pure water, and to provide a diaphragm valve for immediately detecting the leakage from the time when the liquid starts to leak.

In the diaphragm valve, a diaphragm 5 consisting of a body film 5a and a backup film 5b overlapped to the rear of the body film 5a is mounted to a position opposite to a valve seat 3 in a valve body 1 so that wetted surface and rear sides are cut off, and the surface side of the diaphragm 5 is made to contact and separate from the valve seat 3 to open or close a channel. A groove 9 for detecting leakage for detecting leakage by allowing liquid leaked from a damaged section 10 after the body film 5a is damaged to the rear side of the body film 5a to enter for flowing out to the outside of the valve by a capillary phenomenon is formed at the rear side of the body film 5a or the surface side of the backup film 5b.