[Object] To allow a listener to listen to ambient sounds of the external environment in an appropriate manner while wearing a head mounted acoustic device.[Solution] Provided is a signal processing device including a first acquiring unit configured to acquire a sound collection result for a first sound propagating in an external space, a second acquiring unit configured to acquire a sound collection result for a second sound propagating in an internal space, a first filter processing unit configured to generate a difference signal which is substantially equal to a difference between the first sound propagating directly from the external space toward the inside of the external ear canal and the first sound propagating from the external space to the internal space via the mounting unit on the basis of the sound collection result for the first sound, a subtracting unit configured to generate a subtraction signal obtained by subtracting a first signal component based on the sound collection result for the first sound and a second signal component based on an input acoustic signal from the sound collection result for the second sound, a second filter processing unit configured to generate a noise reduction signal based on the subtraction signal, and an adding unit configured to add the difference signal and the noise reduction signal to the input acoustic signal and generate a drive signal.