To provide a wheel alignment adjusting device adjusting a caster angle by carrying out minute adjusting or stepless adjusting, and suppressing a load transmitted to an adjusting part while sufficiently ensuring an adjusting range of the caster angle.

The wheel alignment adjusting device is composed of: an upright 12 mounted to a wheel hub; an arm 2 extending from a vehicle body side in a vertical direction of the upright; a connecting means connecting the upper and lower sides of the upright on an end side of the arm; and an adjusting means provided on at least one of the upper and lower connecting means and adjusting the movement of the connecting means in a vehicle body fore-and-aft direction. The connecting means connects the upright to the arm by a universal joint rotatable in the vehicle body fore-and-aft and lateral directions, and the universal joint is composed of a sphere and a sphere receiving hole surrounding the outer periphery of the sphere.