To provide a microchannel device capable of making a fluid flow through a microchannel or a microchamber without drawing in any air bubbles.

In the microchannel device having the microchannel or the microchamber for making the fluid flow and having a section in which the fluid flows through the microchannel or the microchamber in the direction opposite to the direction of a gravitational force, the width of a cross-sectional shape of the microchannel or the microchamber through which the fluid flows in the direction opposite to the direction of the gravitational force is preferably between 1 m and 1 mm, and its depth is between 1 m and 1 mm.