To prevent impurities such as organic ones from entering when introducing clean room air into a washing chamber, and at the same time efficiently unload air in the washing chamber even when a substrate is being rotated speedily.

In the washing device that at least has a washing chamber 101 being shielded from the fresh air, and washes a substrate 109 in the washing chamber 101, pressure in the washing chamber 101 is reduced as compared with the atmospheric pressure, thus allowing air to flow in a fixed direction from the upper portion to the lower one in the washing chamber 101 and efficiently unloading air when the substrate 102 is being rotated speedily.