A gait training method that can adjust the target load for a trainee is required to meet various demands for training. In this paper, a leg load increase training method using a soft gait-assistive suit is proposed. The soft gait-assistive suit is a power assistive device that helps a trainee walk by actuating a pneumatic artificial rubber muscle (PARM) attached to the trainee’s leg. In the proposed leg load increase training, an external force acting as a load is applied to the trainee’s leg using the suit so that the muscle activity increases throughout the gait cycle. We focused on the trainee’s joint torque trajectories during walking, and the PARMs are actuated to increase them. The effectiveness of the proposed training method was verified by gait experiments on two trainees using a treadmill. The leg electromyogram (EMG) of the trainee wearing the gait-assistive suit was measured, and its change caused by the applied load was observed. From the experimental results, we confirmed that the proposed training method increased the load of the hip extension and flexion of the two trainees, and the load of ankle dorsiflexion of one trainee.