A valve device includes: a driving source making rotational motion; a rotated part provided rotatably around a predetermined axis; and a fluid passage portion having a flow hole for passing a fluid. The valve device further includes: a gear mechanism having gears to transmit rotational motion of the driving source to the rotated part by engagement between the gears to rotate the rotated part; and a biasing part biasing the rotated part toward one side in a circumferential direction with the predetermined axis at the center. The rotated part includes a rotor increasing or reducing an opening of the flow hole in conjunction with rotation of the rotated part and is rotated according to rotational motion of the driving source while being biased toward the one side in the circumferential direction by the biasing part.