PURPOSE: To easily install a suspension arm member on a car body by suppressing the interferences of the suspension arm supporting member for the casing of a rear wheel steering device.

CONSTITUTION: A rear wheel steering device for a vehicle which steers rear wheels by an actuator consisting of a hydraulic motor 40, etc., is equipped with the left and right suspension arm supporting members 33 and 34 in pair which are supported in swingable manner, having a supporting shaft 32 as fulcrum and drive shift, being driven by a driving lever 35, and a connecting member 44 which is connected at the top edge part of the suspension arm consisting of lateral links 13L and 13R through a spherical coupling. Further, installation is performed by inserting the shaft part of a screw shaft 48, etc., installed on the connecting member 44, into the installation holes 43 formed on the suspension arm members 32 and 33.