A driven rotational body rotates relative to a driving rotational body to change a rotational phase therebetween and brings its driven-side stopper wall into contact with a driving-side stopper wall of the driving rotational body in the relative rotational direction. The planetary gear performs a planetary motion while being meshed with the driving rotational body and the driven rotational body to change the rotational phase. The driving rotational body includes a gear member, a cover member, and a fastening member. The gear member has the driving-side stopper wall and is meshed with the planetary gear. The cover member covers an accommodation space, in which the driven rotational body and the planetary gear are accommodated, together with the gear member. The fastening member axially fastens the gear member with the cover member.