To provide a drain cock with a detecting means and a valve element integrated together for detecting the amount of drain and for discharging the drain, respectively, thus achieving a compact form.

A cock body 2 is composed of a cylinder 3 having an inner hole 11 communicated with the bottom face of an air tank and an inward flange 4 provided at the lower end of the cylinder 3 and having a discharge passage 12 communicated with the inner hole 11. In the inner hole 11, a valve element 5 is arranged for opening and closing the discharge passage 12. A pair of electrodes 7a, 7b are provided in the cylinder 3 and exposed to the inner hole 11.