To provide a nucleus effect inhibitor which allows the free selection of colors in coloring a crystalline resin by including the nucleus effect inhibitor which lowers the temperature and rate of crystallization of the crystalline resin, a crystalline resin containing the nucleus effect inhibitor and a method of control of crystallization using the nucleus effect inhibitor.

The nucleus effect inhibitor is composed of a compound which controls the crystallization of a crystalline resin in the crystalline resin. The compound has a basic skeletal structure expressed by formula (1) and formula (2). The crystalline resin contains the nucleus effect inhibitor. The method for controlling crystallization uses the nucleus effect inhibitor. In formula (1) and formula (2) A, B, R1 and R2 are each independently a condensation ring consisting of a single ring or double rings.