In a network system of this invention including a plurality of network devices that transfer frames by repeating, in a constant cycle, a reserved transfer interval that is a time band, in which a frame is transferred with a reservation and a free transfer interval that is a time band, in which a frame is freely transferred, a relay network device that links a first network device that is a transmission source of a frame and a second network device that is a transmission destination of the frame and the first network device execute a reservation processing such that the same time band within the reserved transfer interval is reserved and transfer the frame from the first network device to the second network device on the basis of the reservation result.