The valve opening/closing timing control device includes: a driving rotating body; a driven rotating body; a fixed shaft portion; a fluid pressure chamber; a partitioning portion; and a phase control unit for controlling a rotation phase by supplying/discharging pressurized fluid to/from an advancing chamber or a retarding chamber via an inside of the fixed shaft portion. The driven rotating body has: an inner circumferential member with a cylindrical portion, and a coupling plate portion of the camshaft, the cylindrical portion and the coupling plate portion being integrated with each other; and an outer circumferential member provided with the partitioning portion. The outer circumferential member includes the inner circumferential member in a unified manner so as to have the same rotational axis. The inner circumferential member is formed with an iron-based material. The outer circumferential member is formed with a material that is lighter in weight than the iron-based material.