an apparatus is provided to estimate a gradient of a road surface on which a vehicle travels . the apparatus comprises acquisition , estimation , and compensation members . the acquisition member acquires at least one of acceleration of the vehicle calculated on changes in a travel speed of the vehicle and acceleration sensed from a force applied to the vehicle . the estimation means estimates the gradient of the road surface based on the acquired acceleration . the compensation member compensates the acquired acceleration in terms of influence of noise superposed on the acceleration , depending on an operational condition of the vehicle . the compensated acceleration is used by the estimation . the compensation is carried out by cutting off the noise by a filter , for example .