An active noise reduction device is used with a secondary noise source that generates a secondary noise and an error signal source that outputs an error signal corresponding to a residual sound caused by interference between the secondary noise and a noise. A µ-adjustment unit calculates a step-size parameter for updating a filter coefficient of an adaptive filter by multiplying a standard step-size parameter by a ratio of a standard representative input value corresponding to amplitude of a signal to a representative input value corresponding to the amplitude of the signal.