It is a microfluidic device including a flowchannel in which liquid flows. The flowchannel includes a main channel and a pair of branch channels provided across the main channel from each other to be each connected to the main channel. The main channel includes a first zone, a second zone, and a coupling zone that connects the first zone and the second zone. The second zone is smaller than the first zone in a distance between a bottom surface and a ceiling surface. The coupling zone is configured such that the distance between the bottom surface and the ceiling surface thereof gradually decreases towards the second zone from the first zone. A connection zone provided in the main channel and connected to each of the pair of branch channels overlaps with the coupling zone.