Abstract: An alcohol concentration detecting device for a vehicle includes an alcohol sensor to detect alcohol component contained in an expiration of an occupant of the vehicle, a gas sensor to detect gas components other than the alcohol component contained in the expiration, and a controller to calculate alcohol concentration based on detection value of the alcohol sensor. The controller corrects the calculated alcohol concentration based on detection value of the gas sensor. The alcohol sensor and the gas sensor are configured to further detect a state of air in a passenger compartment of the vehicle.