A method for estimating a road surface state, the method estimating the current road state on which a vehicle is running at one of predetermined road states based on a sound detection signal from a ground contact surface sound detection unit for detecting a sound in the vicinity of the ground contact surface of the tire of the running vehicle, comprising the steps of: calculating a wave profile of frequency dispersion as said sound detection signal by executing a 1/N octave analysis of said detected sound during the vehicle being running, and determining whether said calculated wave profile of frequency dispersion (hereinafter referred to as a "measured wave profile") satisfies predetermined determination conditions of the respective road surface states to estimate the road surface state, wherein a microphone arranged in a container is used to detect said sound, and said determining step is adapted to apply said determination conditions to said measured wave profile including a resonance caused by the container, characterised in that a first determination condition is such that a minimum value of a sound pressure of a band having higher frequency than a band including a frequencies of said resonance caused by the container (hereinafter referred to as a "container resonance frequency band") is larger than a minimum value of a sound pressure of a band having lower frequency than the container resonance frequency band; a second determination condition is such that five frequency bands including a band where the sound pressure is the smallest out of bands having lower frequency than the container resonance frequency band contain two bands where the sound pressure is minimal or minimum; a third determination condition is such that a sound pressure of a band having a second lowest frequency is larger than sound pressures of any other band having lower frequencies than the container resonance frequency band; a forth determination condition is such that the container resonance frequency band is referred to as a band X, a band having the lowest frequency among bands having higher frequencies than the container resonance frequency band having a lower sound pressure than a minimum sound pressure of the bands having lower frequency than the container resonance frequency band is referred to a band Y, and all bands between the band X and the band Y have higher sound pressures than a straight line connecting the sound pressures of the bands X and Y; and the road surface state is estimated with at least one of the first to forth determination conditions. calculating a wave profile of frequency dispersion as said sound detection signal by executing a 1/N octave analysis of said detected sound during the vehicle being running, and determining whether said calculated wave profile of frequency dispersion (hereinafter referred to as a "measured wave profile") satisfies predetermined determination conditions of the respective road surface states to estimate the road surface state, wherein a microphone arranged in a container is used to detect said sound, and said determining step is adapted to apply said determination conditions to said measured wave profile including a resonance caused by the container, characterised in that a first determination condition is such that a minimum value of a sound pressure of a band having higher frequency than a band including a frequencies of said resonance caused by the container (hereinafter referred to as a "container resonance frequency band") is larger than a minimum value of a sound pressure of a band having lower frequency than the container resonance frequency band; a second determination condition is such that five frequency bands including a band where the sound pressure is the smallest out of bands having lower frequency than the container resonance frequency band contain two bands where the sound pressure is minimal or minimum; a third determination condition is such that a sound pressure of a band having a second lowest frequency is larger than sound pressures of any other band having lower frequencies than the container resonance frequency band; a forth determination condition is such that the container resonance frequency band is referred to as a band X, a band having the lowest frequency among bands having higher frequencies than the container resonance frequency band having a lower sound pressure than a minimum sound pressure of the bands having lower frequency than the container resonance frequency band is referred to a band Y, and all bands between the band X and the band Y have higher sound pressures than a straight line connecting the sound pressures of the bands X and Y; and the road surface state is estimated with at least one of the first to forth determination conditions.