The invention has an object of providing an exercise assisting device which allows the user's thigh to contract while having a simple structure with low manufacturing cost. The device comprising a seat member and a seat drive unit. The seat member has a bearing surface configured to support buttocks of a user with one' feet placed on a predetermined foot rest. The seat drive unit is configured to activate a driving source to displace the seat member in such a manner as to vary a user's own weight acting on legs of the user. The seat drive unit swings the seat member at least along a lateral direction.