A fluid handling device includes a first channel, a second channel, and a valve disposed at a connection part between the first channel and the second channel. The valve include a partition wall disposed between the first channel and the second channel, and a diaphragm disposed so as to face the partition wall, a portion of the first channel, and a portion of the second channel. The diaphragm is configured in such a way that when no pressure is applied to the diaphragm, a gap, which serves as a third channel that allows the first channel and the second channel to communicate with each other, is formed between the diaphragm and the partition wall. In plan view, the length of the diaphragm in the extending direction of the third channel is longer than the length of the diaphragm in the direction orthogonal to the extending direction.