This paper presents a new method to estimate an along-wind load that contains a mean component using an equivalent-input-disturbance approach. An along-wind force contains both mean and fluctuating components. However, most studies estimate only fluctuating components. Moreover, these studies assume that the damping matrix is a Rayleigh one. In contrast, this paper presents a method that estimates both the mean and fluctuating components using velocity response. Furthermore, this method does not require that the damping coefficient is Rayleigh damping. The numerical verification verifies using an 11 degree-of-freedom(DOF) model of a seismicisolated building. The results presented that the presented method accurately estimates an along-wind load.