A noise reduction device includes a noise controller, a control sound output component and a residual sound detector. The noise controller is configured to produce a control sound signal for canceling out noise. The control sound output component is configured to output a control sound based on the control sound signal produced by the noise controller. The residual sound detector is configured to detect a residual sound produced by superposition of noise and the control sound outputted from the control sound output component. The control sound output component and the residual sound detector are housed in the shell. The control sound output component and the residual sound detector are away from a rear face of the seat.