The aim of this study is to develop a novel soft exosuit called inflatable assist clothing (InAC) with lightweight and flexible inflatable actuators (IfAs) and to propose a voluntary control method to control the IfA using electrical changes during muscle activity. The InAC is equipped with IfAs, which generate a contraction force by supplying compressed air from a DC vacuum pump with compressor function to assist with knee flexion and extension. In addition, our proposed control method, the bioelectrical signal (BES)-based control algorithm, estimates the desired air volume to be supplied by the DC pump to each individual IfA on the basis of the displacement volume of the BES and then performs feedback control to track the desired air volume. In this study, the control verification experiments were conducted to investigate whether the compressed air volume discharged toward the IfA was changed by using the BES measured from the rectus femoris muscle. The results indicated that the proposed algorithm embedded in the InAC can control the internal air volume of the IfA on the basis of the BES displacement while also tracking the desired air volume (mean absolute error: 3.03 mL; mean absolute percentage error: 6.85%).