As passages forming a main gas passage, each of the passage blocks 3 has a first inverted-V passage, a first outlet passage communicating between the apex of the first inverted-V passage and an outlet of a first on-off valve. As passages forming a vent gas passage, each of the passage blocks 3 has a second inverted-V passage and a second outlet passage communicating between the apex of the second inverted-V passage and an outlet of a second on-off valve. As passages forming a first sub-gas inflow passage, each of the passage blocks has a first inlet passage leading to an inlet of the first on-off valve and a common inlet passage. As passages forming a second sub-gas inflow passage, each of the passage blocks has a second inlet passage leading to an inlet of the second on-off valve and a communication path continued to the common inlet passage.