A sit-up exerciser having a secondary purpose of promoting a bowel movement. Two pivot plates correspondingly pivot, a waist support plate is disposed between the pivot plates to prevent the waist from slipping, and the pivoting angle of the pivot plates can be easily adjusted, so that a person who needs to exercise his or her waist can easily exercise it while having his/her bowel movement facilitated in order to promote the health. The pivoting angle of the pivot plates can be easily adjusted to control the intensity of the exercise, the pivoting speed of the pivot plates can be adjusted to be fast or slow, the temperature of the pivot plates can be adjusted from room temperature up to 70° C. so that the temperature of the surface of the pivot plates can be controlled, and the operating time can be adjusted depending on user's preference.