Hydraulic pressure control device and its mounting method

The purpose of the present invention is to eliminate a delay factor of a construction stage by eliminating the need to interrupt constructing operation for a building when a hydraulic pressure control unit of a nuclear reactor is carried in. The hydraulic pressure control unit comprises the part of a nitrogen gas container 1 which contains high-pressure nitrogen gas, an accumulator 2 which accumulates high-pressure water, a scram valve 3 which is instantaneously opened when a control rod of a control rod driving mechanism is inserted in emergency to release the high-pressure water in the accumulator, and a piping 4 which connect them as unit members. A wall metal plate 20 and floor metal plate 21 for installing and fixing the unit members to the wall 9a and floor 9b of a hydraulic pressure control unit chamber 9 of a nuclear reactor building are constituted as integrated support metal plate 17. This support metal plate 17 and unit members are built in one body.