A valve timing controller includes a first housing (20), a second housing (30) and a bladed rotor (40). An outer diameter (D1) of an open end portion (32) of the second housing is adjusted to a predetermined value, that a mechanical interference with an annular component (93) can be prevented. The second housing has a lower end portion opposite to the open end portion and a reinforcing part (34), which is a radially outer portion of a corner part (p1) of a flow chamber and a delay chamber adjacent the lower end portion. A thickness (t1) of the reinforcing part in a radial direction is greater than that of the other cylindrical part of the second housing. An outer diameter (D2) of the reinforcing member is greater than the predetermined value.