When a throttle is substantially fully open and startup is not underway, a CVT control unit (20) controls a speed ratio in accordance with a fully open speed change line. When the throttle is substantially fully open and startup is underway, the CVT control unit (20) controls the speed ratio in accordance with a fully open startup speed change line. When the throttle is substantially fully open, startup is underway, and the number of times the primary pulley rotation speed exceeds a belt assurance upper limit value exceeds an assurance frequency number, the CVT control unit (20) controls the speed ratio in accordance with the full throttle speed change line instead of the full throttle startup speed change line, even though the throttle is substantially fully open and vehicle startup is underway.