A noise reduction device includes: a noise detector that detects noise in a space at least partially surrounded by a shell; a noise controller that generates a control sound signal for reducing the noise detected by the noise detector; and a control sound outputter that outputs control sound to the space based on the generated control sound signal. A seat that is reclinable including a recliner having a seat surface at a variable angle with respect to a reference plane is provided in the space. When L (cm) represents the length of the recliner in the front-to-back direction, the control sound outputter is provided at a height of L×sin θ+8 (cm) above the reference plane where θ is between two degrees and eight degrees, inclusive.