A rear wheel steering apparatus for a vehicle, the rear wheel steering apparatus configured to be mounted on a suspension mechanism that supports rear wheels (RL, RR) of the vehicle and steering the rear wheels (RL, RR), the rear wheel steering apparatus comprising: a housing configured to be connected via a first connection member and a second connection member to the suspension mechanism; an electric motor accommodated within the housing; a planetary gear mechanism including a sun gear connected to an output shaft of the electric motor, a ring gear supported within the housing to be non-rotatable, a planetary gear meshing with the ring gear and the sun gear, and a carrier connected to the planetary gear, the planetary gear mechanism decelerating an output of the electric motor; a linear motion mechanism including a nut member connected to the planetary gear mechanism and constituting the carrier, and a rod threadedly engaged with the nut member and connected to the second connection member, the linear motion mechanism converting a rotary motion of the nut member to a linear motion of the rod, the housing including a cylindrical body which accommodates the electric motor and the planetary gear mechanism in a state where the electric motor and the planetary gear mechanism are arranged in tandem with each other and which includes a lock portion provided at an inner surface of the cylindrical body to be positioned between the electric motor and the planetary gear mechanism, the housing including a connection cover including the first connection member and closing an opening portion of the cylindrical body; a cylindrical holding member holding the ring gear within the cylindrical body in a state where the ring gear constituting the planetary gear mechanism is prevented from rotating; and a bearing supporting the nut member in a manner that the nut member is rotatable relative to the cylindrical holding member, wherein the bearing and the cylindrical holding member are disposed and held between the lock portion of the cylindrical body and the connection cover, and the cylindrical holding member is held to be non-rotatable relative to the cylindrical body. a housing configured to be connected via a first connection member and a second connection member to the suspension mechanism; an electric motor accommodated within the housing; a planetary gear mechanism including a sun gear connected to an output shaft of the electric motor, a ring gear supported within the housing to be non-rotatable, a planetary gear meshing with the ring gear and the sun gear, and a carrier connected to the planetary gear, the planetary gear mechanism decelerating an output of the electric motor; a linear motion mechanism including a nut member connected to the planetary gear mechanism and constituting the carrier, and a rod threadedly engaged with the nut member and connected to the second connection member, the linear motion mechanism converting a rotary motion of the nut member to a linear motion of the rod, the housing including a cylindrical body which accommodates the electric motor and the planetary gear mechanism in a state where the electric motor and the planetary gear mechanism are arranged in tandem with each other and which includes a lock portion provided at an inner surface of the cylindrical body to be positioned between the electric motor and the planetary gear mechanism, the housing including a connection cover including the first connection member and closing an opening portion of the cylindrical body; a cylindrical holding member holding the ring gear within the cylindrical body in a state where the ring gear constituting the planetary gear mechanism is prevented from rotating; and a bearing supporting the nut member in a manner that the nut member is rotatable relative to the cylindrical holding member, wherein the bearing and the cylindrical holding member are disposed and held between the lock portion of the cylindrical body and the connection cover, and the cylindrical holding member is held to be non-rotatable relative to the cylindrical body.