A wakefulness inducing device includes: a heat dissipation intensity obtainer obtaining a user's heat dissipation intensity from a heat dissipation intensity sensor; and a controller controlling an air conditioner to alternate the user's heat dissipation intensity between a first heat dissipation intensity and a second heat dissipation intensity lower than the first heat dissipation intensity. The controller alternates the user's heat dissipation intensity by controlling the air conditioner based on the user's heat dissipation intensity to set a first time period longer than a second time period. In the first time period, the user's heat dissipation intensity increases from the second heat dissipation intensity to the first heat dissipation intensity, or remains at the first heat dissipation intensity. In the second time period, the user's heat dissipation intensity decreases from the first heat dissipation intensity to the second heat dissipation intensity, or remains at the second heat dissipation intensity.