The objective of the present invention is to provide an amphibious vehicle and a method of controlling the attitude of the vehicle body of an amphibious vehicle, with which it is possible to reduce the fluid resistance when traveling on water and to improve the propulsion performance of the vehicle main body. An amphibious vehicle 1 according to the present invention is characterized in being provided with: a vehicle main body 11 capable of moving on water and on land; a rear flap 14B provided at the rear of the vehicle main body 11; a drive unit 33 which drives the rear flap 14B to vary a flap angle θ1 between the vehicle main body 11 and the rear flap 14B; a detecting unit 31 which detects a trim angle of the vehicle main body 11, a vehicle speed and the flap angle θ1; and a control unit 32 which controls the flap angle θ1 on the basis of the trim angle, the vehicle speed and the flap angle θ1 detected by the detecting unit 31.