The utility model provides a sex assistant device, which is a unit completed by assembling motors and other mechanical devices. When the motor is started to rotate, the stretching bar within the unit is motivated along with the penis to perform automatically repeated mechanical movements so that the wife (female) will first achieve a certain degree of joy. Then the husband (male) makes love to the wife so that the wife (female) and the husband (male) will easily access to sexual climax, which will relatively increase the marital delight to build a happy family life.