To judge a road surface in a short time simplify preparations and a control program.

A road surface condition detecting device is provided with a wheel speed detecting means (a) which detects the speed of at least one of plural wheels; a vehicle speed change detecting means (b) for detecting the amount of change in the wheel speed in a predetermined time; a change calculating means (c) for calculating the absolute values of the amounts of changes in the wheel speed; a road surface judging means (d) which, when the calculation value obtained by the change calculating means (c) is equal to or greater than a predetermined threshold, judges a road surface to be in a bad condition and which if the value is less than the threshold judges the road surface to be not bad; and a low-pass filter (e) by which signals input from the change calculating means (c) are cut off at frequencies at least higher than unsprung resonance frequency.