PURPOSE: To reduce cost to a large extent and to shorten a term of works to a large extent by dispensing with compacting work and ageing by reducing the pressure in a form in such a state that concrete not hardened is cast.

CONSTITUTION: As first, concrete 2 not hardened is poured into a form 1 and the form 1 having this concrete 2 not hardened poured thereinto is received in a contractable bag like container 3 to be hermetically sealed by the container 3. A vacuum pump 4 is connected to the bag like container 3 to evacuate the form 1. Since the form 1 is evacuated, the b.p. in the form 1 lowers and the moisture in the concrete 2 not hardened is evaporated. By this mechanism, the concrete 2 not hardened is solidified to be molded within the form. Therefore, ageing becomes unnecessary.