A spring prime mover unit comprising a spring prime mover, a transmission gear and a plurality of connectors. Among the connectors, there are rotatable connectors and non-rotary connectors. The rotatable connectors are the ends of some shafts of the transmission gear and the non-rotary connectors are the attachments of a covering frame. The spring prime mover unit may be exchangeably equipped with auxiliary toy parts or toys which have not prime movers and form various movable toys to one prime mover unit. Therefore, children themselves can assemble various interesting movable toys and enjoy various motion of the toys.