A valve timing controller includes a first rotary element having a first gear part, a second rotary element having a second gear part, and a planetary gear including a third gear part and a fourth gear part which respectively engage with the first gear part and the second gear part. The planetary gear performs a planetary motion to vary a relative rotational phase between the first rotary element and the second rotary element. The valve timing controller further includes a supporting member supporting the planetary gear in such a manner that the planetary gear is slidable in its axial direction between the first rotary element and the second rotary element, and an elastic member restricting a displacement of the planetary gear in its axial direction.