An air blowing device, comprising: a casing having an outside air inlet through which air outside a cabin is introduced as air-conditioning air, and an inside air inlet through which air inside the cabin is introduced as the air-conditioning air; an inside/outside air switching door which opens and closes the outside air inlet and the inside air inlet ; and a door drive unit which drives the inside/outside air switching door , the air blowing device being mounted on a vehicle, and blowing the air-conditioning air, wherein the casing is divided into a front casing member and a rear casing member at a center portion of the casing in the lengthwise direction of the vehicle, a filter insertion hole through which a filter for filtering the air-conditioning air is inserted into the casing is formed through a rear wall of the rear casing member , the outside air inlet and the inside air inlet of the casing extend in a lengthwise direction of the vehicle, the inside/outside air switching door has a rotating shaft which extends in the lengthwise direction of the vehicle, and is rotatably supported by the casing , the rotating shaft being provided with an open/close plate which opens and closes the outside air inlet and the inside air inlet , the door drive unit is attached to a portion of the rear wall of the rear casing member , the portion being positioned above the filter insertion hole , and the door drive unit is coupled to the rotating shaft of the inside/outside air switching door , a first passage and a second passage, through each of which the air-conditioning air flows, are arranged one above the other in a vertical direction in the air blowing device , each of the first and second passages communicating with the outside air inlet and the inside air inlet , and a first fan and a second fan, each of which blows the air-conditioning air, are respectively arranged in the first and second passages. a casing having an outside air inlet through which air outside a cabin is introduced as air-conditioning air, and an inside air inlet through which air inside the cabin is introduced as the air-conditioning air; an inside/outside air switching door which opens and closes the outside air inlet and the inside air inlet ; and a door drive unit which drives the inside/outside air switching door , the air blowing device being mounted on a vehicle, and blowing the air-conditioning air, wherein the casing is divided into a front casing member and a rear casing member at a center portion of the casing in the lengthwise direction of the vehicle, a filter insertion hole through which a filter for filtering the air-conditioning air is inserted into the casing is formed through a rear wall of the rear casing member , the outside air inlet and the inside air inlet of the casing extend in a lengthwise direction of the vehicle, the inside/outside air switching door has a rotating shaft which extends in the lengthwise direction of the vehicle, and is rotatably supported by the casing , the rotating shaft being provided with an open/close plate which opens and closes the outside air inlet and the inside air inlet , the door drive unit is attached to a portion of the rear wall of the rear casing member , the portion being positioned above the filter insertion hole , and the door drive unit is coupled to the rotating shaft of the inside/outside air switching door , a first passage and a second passage, through each of which the air-conditioning air flows, are arranged one above the other in a vertical direction in the air blowing device , each of the first and second passages communicating with the outside air inlet and the inside air inlet , and a first fan and a second fan, each of which blows the air-conditioning air, are respectively arranged in the first and second passages. <EOS>