A hopper for cleaning a coating machine in which a rotary atomizing head extends through an opening in the upper surface of a hopper housing, a thinner for cleaning the rotary atomizing coating machine and a residual coating material are sprayed on the inside, an airstream control member for preventing flow from ascending from the inside of the housing to the outside of the housing through a gap between the coating machine and the opening by the rotation of the rotary atomizing head corresponding to the gap between the coating machine and the opening, and the control member is formed with an air vent hole for supplying air to a negative pressure zone formed just below the rotary atomizing head.