To clean an internal face of a hopper putting a ready-mixed concrete into a rotary drum of a concrete mixer truck without using washing water.

In a cleaning method for an internal face of a hopper provided with an inlet and discharge port of the ready-mixed concrete for supplying the ready-mixed concrete into the rotary drum which is installed at the rear of the concrete mixer truck, this method is characterized by ejecting an airflow in the same direction along a feeding direction to the rotary drum of the ready-mixed concrete from the neighborhood of the inlet of the hopper, transferring the ready-mixed concrete deposited at the internal face of the hopper toward the rotary drum and discharging the ready-mixed concrete from the discharge port.