To reuse effectively return concrete or remaining concrete without decreasing physical properties of a cement composition by preventing lowering of fluidity of the cement composition by a method wherein a fluidity-retaining agent is added before quick low temperature cooling.

As cement, only if it is hardened by being reacted with water, it suffices basically, and various kinds of mixed cement or the like of various kinds of Portland cement or the like can be used. As a means wherein an unhardened cement composition is rapidly cooled, a freezing chamber, a refrigerator, or a method of using liquid nitrogen, etc., and exemplified. Further, for cooling speed and temperature of the cement composition, it is preferably cooled quickly as for as possible at low temperature in order to delay or stop hydration reaction with cement contained in the cement composition. Therefore, in a method wherein the cement composition is warmed after quick cooling and storing for a long time at low temperature, the cement composition having excellent fluidity can be obtained.