PURPOSE: To charge the gap of a concrete secondary product such as concrete panel with concrete mortar, in s simple manner with high workability.

CONSTITUTION: Cement and sand are added into water, and concrete mortar is formed by the kneading by a small-sized stirrer 11, etc., having an agitating blade 14 at the top end of a rotary shaft 13. A spray gun 1 is charged with concrete mortar, and a small-sized compressor 8 is connected with the spray gun 1, and in this state, the spray nozzle 3 of the spray gun 1 is approached to the gap of a concrete secondary product. Air is supplied at a low pressure and a low flow rate from the small-sized compressor 8, and concrete mortar is allowed to flow out from the spray nozzle 3 without splashing the concrete mortar, and the gap of the concrete secondary product is charged.