PURPOSE: To simplify execution by connecting a water main side to the outside, and connecting a water gauge unit consisting of a water gauge and a check valve and capable of reduction to a base section connecting the water gauge unit to the inside with one touch.

CONSTITUTION: A detachable device 1 is constituted of a base section 2 and a water gauge unit 3 combined with a check valve 4 as a unit. The unit 3 is constituted of a main connection pipe 10 provided with a water gauge M, an auxiliary connection pipe into which the check valve 4 is incorporated and a spring 13. After that, the pipe 10 and a pipe 12 are linked and connected through a cylinder section, a piston section 11 and the spring 13 so that they are capable of expansion. Then, hooks 17 and 20 of the unit 3 are held by using detachable jigs to shorten the unit 3, and the base section 2 and the unit 3 are detached through connection ports 5x and 5y of the base section 2 connection plates 6x and 6y, connection ends 7x and 7y of the unit 3 and pressure welding sections 8x and 8y. According to the constitution, execution can be simplified.