A rear wheel steering apparatus for a vehicle configured to be provided at a suspension mechanism supporting a rear wheel of the vehicle and for steering the rear wheel, the rear wheel steering apparatus comprising: a housing configured to be connected to the suspension mechanism via a first connection member and a second connection member, the housing including a cylinder portion and a casing; an electric motor housed in the cylinder portion; a speed reduction mechanism housed in the cylinder portion and reducing speed of an output of the electric motor; a linear motion mechanism including a nut member rotatably connecting to the speed reduction mechanism and a rod threadingly engaged with the nut member and connecting to the second connection member, the linear motion mechanism converting a rotation of the nut member to a linear motion of the rod; the casing including at least one opening portion (12x, 12y) that opens in parallel to the rod and a communication hole provided separately from the opening portion (12x, 12y), the casing positioned surrounding the rod extending from the cylinder portion and being fixed to the cylinder portion; a cover member (15, 16) joined to the casing to seal the opening portion (12x, 12y) of the casing; and a controller housed in the casing and controlling an actuation of the electric motor; characterized by further comprising: a power line (80a, 80b) and a signal line electrically connected to the controller in the casing; a thermal shrinkage tube surrounding the power line (80a, 80b) and the signal line to retain thereof; and a support bracket housing the power line (80a, 80b) and the signal line and liquid-tightly joined to the casing at the communication hole; wherein the power line (80a, 80b) and the signal line are liquid-tightly supported in the communication hole of the casing via the thermal shrinkage tube; an adhesive agent is filled in the thermal shrinkage tube between the power line (80a, 80b) and the signal line; and the thermal shrinkage tube is attached to surround a portion where the power line (80a, 80b) and the signal line are lead from the support bracket to the outside. a housing configured to be connected to the suspension mechanism via a first connection member and a second connection member, the housing including a cylinder portion and a casing; an electric motor housed in the cylinder portion; a speed reduction mechanism housed in the cylinder portion and reducing speed of an output of the electric motor; a linear motion mechanism including a nut member rotatably connecting to the speed reduction mechanism and a rod threadingly engaged with the nut member and connecting to the second connection member, the linear motion mechanism converting a rotation of the nut member to a linear motion of the rod; the casing including at least one opening portion (12x, 12y) that opens in parallel to the rod and a communication hole provided separately from the opening portion (12x, 12y), the casing positioned surrounding the rod extending from the cylinder portion and being fixed to the cylinder portion; a cover member (15, 16) joined to the casing to seal the opening portion (12x, 12y) of the casing; and a controller housed in the casing and controlling an actuation of the electric motor; a power line (80a, 80b) and a signal line electrically connected to the controller in the casing; a thermal shrinkage tube surrounding the power line (80a, 80b) and the signal line to retain thereof; and a support bracket housing the power line (80a, 80b) and the signal line and liquid-tightly joined to the casing at the communication hole; wherein the power line (80a, 80b) and the signal line are liquid-tightly supported in the communication hole of the casing via the thermal shrinkage tube; an adhesive agent is filled in the thermal shrinkage tube between the power line (80a, 80b) and the signal line; and the thermal shrinkage tube is attached to surround a portion where the power line (80a, 80b) and the signal line are lead from the support bracket to the outside.