To facilitate the work for fitting and removing a valve device to/from a piping element so that a worker can do these work alone by improving workability in these work when performing maintenance of automatic equipment provided with a valve device such as a piston valve device.

A connecting surface 170 provided in the piston valve device V1 is provided with engagement recessed parts 171 and 172, and a connecting surface 30 provided in a piping block 3 is provided with engagement pins 31 and 32. These engagement parts are engaged with each other to fix the valve device V1 and the piping block 3 to a bolt 178 in the condition that connection openings 173, 174 and 175 on the valve device V1 side and connection openings 35, 36 and 37 on the piping block 3 side are connected to each other.