To provide a vehicle heater ensuring a heating function while suppressing window glass fogging, and reducing fuel consumption of an on-vehicle internal combustion engine.

The heater is provided with: a heater core whose interior permits passage of a cooling water of the on-vehicle internal combustion engine; an internal air passage for guiding the air inside a vehicle interior to the heater core; and an external air passage for guiding the air outside the vehicle interior to the heater core. Heating is carried out by heating the air guided through the internal air passage and the external air passage by means of heat exchange between the guided air and the cooling water passing through the interior of the heater core, and then supplying the resulting air into the vehicle interior. Based on a transmission oil temperature THOT (S101), an engine oil temperature THOE (S102), and a cooling water temperature THW (S103), the setting mode of the ratio of the internal air amount and the external air amount is changed (S104, S107).