To control the displacement of a diaphragm for a fine flow channel without requiring any high positioning accuracy.

A micro fluid device includes a diaphragm valve composed of the capillary flow channel 5 and the diaphragm 7 capable of being displaced with respect to the flow channel. A cylindrical guide part 13 is provided at the position of the diaphragm 7 of a third resin layer 4. A steel ball 12 is provided on the diaphragm 7 opposite a wide-width part 6 of the flow channel 5 inside the guide part 13. The diaphragm 7 is accurately displaced through the steel ball 12 only by inserting a slider into the guide part 13, so that the flow channel 5 is open/close-controlled at the wide-width part 6.