There has been arising attention in wearable robots for gait assistance in daily lives. Among various concerns for developing wearable robots, the moment of assistance is of much importance because it considerably affects assistance performance and safety. In this paper, we propose an algorithm that can detect gait phase of the wearer in daily walking conditions, with the natural periodic property of the thigh in gait. With varying gait speed, the suggested algorithm gives identical gait phase value for identical gait event.