A machining method for an integrated piping plate, for example, composed of a plurality of plates joined together, and in which an instrument and a component constituting an apparatus, or the instrument, or the component are or is disposed on one surface or both surfaces of the integrated piping plate, and the instrument and the component, or the instrument, or the component are or is connected by fluid channel grooves formed in joining surfaces of the plates, and communication holes formed in the plates. The machining method welds the joining surfaces of the plates around the entire periphery of the fluid channel grooves, for example, by an FSW welding machine, to join the plates. Compared with joining of the plates by an adhesive, the machining method can increase the durability of the plate joining portion and increase pressure resistance. Also, the method can increase work efficiency and further downsize the integrated piping plate.