To provide an on-vehicle marker capable of preventing any snow and ice deposition and fogging on the marker by blowing hot air into a display unit box of the marker installed on a vehicle roof by utilizing heat radiated from an engine room of a vehicle.

In the on-vehicle marker (1), a hot water feed pipe (5) and a circulating water pipe (6) are arranged between an engine room (3) of the vehicle (X) and a heater unit (2) installed in a rear part in the vehicle (X), a hot air blow-in duct (4) is connected between the heater unit (2) and a display unit box (11) installed on a roof (X') of the vehicle (X), and hot air (a) is blown into the display unit box (11).