This paper proposes a new style of manipulation by a humanoid robot. Focusing on the task of pushing an object, the foot placement is planned in real time according to the result of manipulation of the object. By using the impedance control of the arms, the humanoid robot can stably push the object regardless of the mass of the object. If the object is heavy, the humanoid robot pushes it by walking slowly and vice versa. Also, for planning the gait in real time, we propose a new analytical method where a newly calculated trajectory of the robot motion is smoothly connected to the current one. The effectiveness of the proposed method is confirmed by simulation and experiment