A valve device 1 includes a rotational shaft 2, and a valve body 4 internally forming a space 10 and rotatable about the rotational shaft 2, the valve body 4 having an outer circumferential surface 28 where a first communication hole 36 and a bottomed groove 38 are formed, the first communication hole 36 communicating with the space 10, the bottomed groove 38 extending from the first communication hole 36 toward one side in a rotational direction of the rotational shaft 2, and the groove 38 including a first section 40 in which at least one of a depth D of the groove 38 and a width W of the groove 38 increases toward the first communication hole 36.