Microfluidic device and the broth microdilution method

Providing a variety of easily and reliably microfluidic device having a fine channel structure that can provide it has been equipped with microfluidic dilution internally. Micro-channel structure provided in the substrate 2 has a first mixing unit 11, and a second mixing unit 21 connected to the downstream side of the first mixing unit 11. Each mixing unit 11 and 21 includes first to third micro-channel. The first end of the weighed portion 11d is first micro-channel 11a made of micro channel having a volume equal to the volume of a quantity of a first microfluidic and the other end to the second micro-channel 12 open to provided the merging section 12a. One end of the second weighed portion 13d made of the fine flow path having a volume equal to the volume of a fixed amount of the second microfluidic is connected to the third micro-channel 13, the other end merging section 12a It is open. One of the first to third outlet ports of the first mixing unit is connected to the first or third inlet port of the second mixing unit 21.