PURPOSE: To immediately judge the ovulation period via only an easy self-action on the spot at the action by fitting a judging reaction chemical colored or discolored by the change in a vagina in coincidence with the ovulation period to a judging tool main body to be inserted into the vagina of a woman.

CONSTITUTION: A judging reaction chemical 2 such as a reaction accelerating chemical, a cornification cell stain chemical and a hydrogen ion concentration indicator proportional to the reduction of the cervical canal mucus viscosity is fitted at one end of a judging tool main body 1. The judging tool main body 1 is held with fingers at the holding side, a reaction section at the opposite side is inserted into the vagina of a person under test from the tip, and the judging reaction chemical 2 is colored or discolored based on the reduction of the cervical canal mucus viscosity in the vagina, an increase of the epithelium cell cornification exfoliation quantity, and the rise of the hydrogen ion concentration. The increase of the cervical canal mucus quantity, the reduction of its viscosity, the increase of the epithelium cell cornification exfoliation quantity in the vagina, and the rise of the hydrogen ion concentration are remarkable in coincidence with the ovulation period, thus she can judge whether she is in the ovulation period or not based on the degree of the coloring or discoloring of the judging reaction chemical 2 on the spot at the insertion action herself.