A road surface roughness measuring device which measures a roughness in each direction at the same positions as those sections where a coefficient of dynamic friction is measured by dividing a measurement circle on a road surface where the coefficient of dynamic friction is measured into multiple sections, wherein a frame body (32) having a plurality of legs (31) for installation on a road surface (G) is provided, a rotating shaft (45) extending in vertical direction is provided on the frame body (32), a rotary encoder (44) and a rotary disk (50) are installed at the upper and lower ends of the rotating shaft (45), respectively, a motor with speed reduction gear (39) driving the rotating shaft (45) through gears (41, 41a) is provided, a laser displacement gauge (51) is installed on the rotary disk (50), the laser displacement gauge (51) is installed so that a rotary type dynamic friction coefficient measurer measures a roughness by the rotation of the rotary disk (50) along a measurement circle (P) where a coefficient of dynamic friction was measured, the measurement circle (P) is divided into multiple sections, and the road surface roughness for each divided section (a to h) is calculated based on the signals from the laser displacement gauge (51) and the rotary encoder (44).