An apparatus and method for estimating a step length of a user are provided. The apparatus and method use a step length estimation algorithm, e.g. a step length estimation parameter coefficient, according to a movement state of a user, i.e. whether the movement state is a walking state or a running state. The movement state of the user is determined on the basis of an acceleration variance value of an acceleration signal output from an accelerometer. Accordingly, the apparatus and method prevent errors in step length determinations.