Drying shrinkage reducing agent

The following formula (1): [Formula 1] In the In comprising as an essential component at least one structural unit (I) represented, shrinkage reducing the surface tension at the solution containing 0.2 wt% of the polymer cement supernatant containing polymer is 25 to 50 mN / m agent is provided. The drying shrinkage-reducing agent, to the extent of usage desired drying shrinkage-reducing performance can be obtained, without the dispersibility, the combined use with a dispersant, can be adjusted and the drying shrinkage-reducing property dispersibility according to the purpose.