The dc power feeding system has been attracted attention in recent years. Since the load is dynamically changed in this system, the stability of dc-dc converter is important. This paper presents the stability analysis and the transient response of digital integral gain changeable control dc-dc converter using small output capacitance. The proposed method changes the integral gain with a single logarithm function according to the load current. It is verified the proposed method can obtain a good transient response with high stability even when the output capacitance is small.