We present the vibration control of a self-standing quadrupedal walking robot with one-degree-of-freedom mechanisms which are called YT-mechanisms. Our developed robot walks with trot gait, in which its weight is supported by each pair of diagonally opposite legs alternately. The experimental results show that the natural frequency of first-mode vibration changes with the rotational angle of the mechanisms. The movement of feet's position generates imbalance force which makes the elastic displacement of legs and the vibration during walking. In order to reduce the vibration, we propose to use dynamic absorber as a passive vibration control device and investigate the influence of the tuned frequency of it. Experimental results show the advantages of this method.