To provide a step detector which makes a vision aid for supporting walking by checking the safety of steps for ill-sighted persons in view of the walking aid capacity not obtained sufficiently by the conventional type alone.

In the step detector 1, an ultrasonic road surface height sensor 4 for measuring the height of the road surface from the shoes bottoms is carried on a right sensor part 3 of the right shoe 2 near the tip toe thereof and an ultrasonic type obstacle distance sensor 5 for measuring the distance to the obstacle ahead is carried on the front right end of the shoe. A periodic trigger circuit 7 is activated by the output of an impact sensor 6 to start the measurement. The signal is transmitted to a left sensor part 10 of the left shoe 9 on the radio wave from an FM oscillator 8 and activates a trigger circuit 14 to start the measurements with the road surface height sensor 11 and the obstacle distance sensor 12. The left and right signals are processed by an intermittent oscillator 15 with an audible sound range to convert the large left and right road surface heights to an oscillation frequency and the small left and right distances to the obstacle to an intermittent ratio. The outputs are carried on the radio waves from the FM oscillator 16 to be converted to the intermittent vibration sounds with a radio set 17, and the road surface heights can be recognized from the oscillation frequency while the distance to the obstacle from the intermittent ratio.