To provide a speed suppressing device installed on a road having a vehicle passing zone and a roadside zone and capable of securing the safety of pedestrians and bicycle users passing through the roadside zone by reducing the speed of vehicles passing through the vehicle passing zone.

This speed suppressing device comprises three speed suppressing means 10 each having a restricted zone 11 projecting to the center of the vehicle passing zone 1 to reduce the width of the vehicle passing zone 1 and a separating zone 12 installed at the position opposite to the restricted zone 11 along a road at intervals of approximately three times the overall length of the speed suppressing means 10. The three speed suppressing means 10a, 10b, 10c are disposed so that the restricted zones 11a, 11b, 11c can be disposed in staggered shape along the road, namely, the restricted zones 11a, 11b, 11c can be replaced with the separating zones 12a, 12b, 12c when the vehicles pass through the speed suppressing device.