Abstract: A pipe welding structure includes: a channel plate that includes a fluid channel; through-hole plates stacked on the channel plate, each of the through-hole plates having through holes that communicate with each other and forming a combined through hole; and a pipe inserted into the combined through hole and welded to one of the through-hole plates disposed farthest from the channel plate, the pipe internally including a pipe channel that connects to the fluid channel.

Abstract: A micromixer includes: a first channel plate where a first channel and a plurality of first branch channels are each formed by a non-through groove in a front surface, and a first confluence channel is formed by a non-through groove in a rear surface, and includes a first communication channel that communicates the first branch channels with the first confluence channel; a first lid plate that covers the front surface; a second channel plate where a second confluence channel is formed by a non-through groove in the front surface, and a second channel and a plurality of second branch each formed by a non-through groove in the rear surface, and includes a second communication channel that communicates the second branch channels with the second confluence channel; and a second lid plate that covers the rear surface of the second channel plate.