A wakefulness-maintaining device capable of maintaining a driver's wakefulness by making the driver aware of changes in sound characteristics. A wakefulness-maintaining device (100), which maintains a person's wakefulness, wherein: a switching time control part (102) analyzes the characteristics of perceived sounds acquired by a microphone provided inside the vehicle, the perceived sounds comprising control sounds played back by the wakefulness-maintaining device (100) and environmental sounds around the person when no control sounds are being played back; an in-car sound-accumulating part (103) accumulates the perceived sounds; an acoustic pressure change-setting part (105) sets the control method to be used on the environmental sounds on the basis of the characteristics of the perceived sounds accumulated by the in-car sound-accumulating part (103); and a control sound-generating part (106) applies the control method, set by the acoustic pressure change-setting part (105), on the environmental sounds and generates control sounds.