To reduce members and sealing parts in number in a fluid control device.

The manufacture of a joint member is formed out of a first process for boring either one of a right or a left upward directed opening passage 52a, a communication passage 52b, and an auxiliary passage 52c in a block shaped body 52, a second process for inserting a block member 54 into the auxiliary passage 52c, a third process for welding the block member 54 onto the auxiliary passage 52c, and of a fourth process for boring the other upward directed opening passage 52d in the block shaped main body 52. In the second process, the block member 54 is so designed as to be laid in the forming portion of the other upward directed opening passage 52d.