In a wireless transmission device provided with an adaptive modulation circuit and a control method for the adaptive modulation circuit, an Ethernet signal received from a wired transmission path is transmitted to an opposite station one-to-one via a wireless transmission path and the Ethernet signal in the opposite station is again output to the wired transmission path. A traffic-statistics circuit which accumulates a traffic volume of a time zone-specific Ethernet signal as statistical data is provided. A wireless transmission capacity can be reduced by decreasing a multi-level number of a modulation scheme in a time zone in which the traffic volume is small based on the accumulated statistical data.