A fluid pressure control device for a construction machine including control valves (121, 122, 123, 124, 125, 221, 222, 223, 224) that supply and discharge a working fluid supplied from a first pump and a second pump to and from actuators, the fluid pressure control device, comprising: a first circuit system connected to the first pump, the first circuit system having a first control valve group formed by a first traveling control valve and a first working control valve (122, 123, 124, 125) arranged on the downstream side of the first traveling control valve, a first neutral passage configured to return the working fluid of the first pump into a tank in a case where all the control valves (121, 122, 123, 124, 125) of the first control valve group are placed at a neutral position, and a first parallel passage connected in parallel to the first control valve group; a second circuit system connected to the second pump, the second circuit system having a second control valve group formed by a second traveling control valve and a second working control valve (222, 223, 224) arranged on the downstream side of the second traveling control valve, a second neutral passage configured to return the working fluid of the second pump into the tank in a case where all the control valves (221, 222, 223, 224) of the second control valve group are placed at a neutral position, and a second parallel passage connected in parallel to the second control valve group; and an open/close mechanism configured to open/close the first neutral passage, characterized by a switching valve connected to the first parallel passage and the second neutral passage on the upstream side of the second control valve group, the switching valve having a normal position where the working fluid of the first pump is supplied to the first traveling control valve and the working fluid of the second pump is supplied to the second traveling control valve, a straight travelling position where the working fluid of the first pump is supplied to the first travelling control valve and the second travelling control valve and the working fluid of the second pump is supplied to the first parallel passage and the second parallel passage, and a merging position where the working fluid of the first parallel passage is merged into the second neutral passage; wherein in a case where at least one of the control valves (222, 223, 224), on which merging is required, on the downstream of the second traveling control valve is switched to a position other than the neutral position, by closing the first neutral passage by the open/close mechanism and switching the switching valve to the merging position, the working fluid of the first pump is merged into the working fluid of the second pump for the control valve (222, 223, 224) on which merging is required. a first circuit system connected to the first pump, the first circuit system having a first control valve group formed by a first traveling control valve and a first working control valve (122, 123, 124, 125) arranged on the downstream side of the first traveling control valve, a first neutral passage configured to return the working fluid of the first pump into a tank in a case where all the control valves (121, 122, 123, 124, 125) of the first control valve group are placed at a neutral position, and a first parallel passage connected in parallel to the first control valve group; a second circuit system connected to the second pump, the second circuit system having a second control valve group formed by a second traveling control valve and a second working control valve (222, 223, 224) arranged on the downstream side of the second traveling control valve, a second neutral passage configured to return the working fluid of the second pump into the tank in a case where all the control valves (221, 222, 223, 224) of the second control valve group are placed at a neutral position, and a second parallel passage connected in parallel to the second control valve group; and an open/close mechanism configured to open/close the first neutral passage, characterized by a switching valve connected to the first parallel passage and the second neutral passage on the upstream side of the second control valve group, the switching valve having a normal position where the working fluid of the first pump is supplied to the first traveling control valve and the working fluid of the second pump is supplied to the second traveling control valve, a straight travelling position where the working fluid of the first pump is supplied to the first travelling control valve and the second travelling control valve and the working fluid of the second pump is supplied to the first parallel passage and the second parallel passage, and a merging position where the working fluid of the first parallel passage is merged into the second neutral passage; wherein in a case where at least one of the control valves (222, 223, 224), on which merging is required, on the downstream of the second traveling control valve is switched to a position other than the neutral position, by closing the first neutral passage by the open/close mechanism and switching the switching valve to the merging position, the working fluid of the first pump is merged into the working fluid of the second pump for the control valve (222, 223, 224) on which merging is required.