An air conditioner comprising: an air duct; and a heat exchanger unit to be disposed inside a building, the heat exchanger unit comprising: a casing having a duct to be flown through by air, a first connection connected to the air duct for communicating the heat exchanger unit with the outside of the building and a second connection connected to the air duct again for leading to the outside of the building, a fan disposed in the casing and configured to induce a flow of the air through the duct in a flow direction, a heat exchanger being V-shaped in side view with an apex at one end and an opening at the opposite end, the heat exchanger being disposed in the duct with the apex directed towards the first connection and facing the air flow, wherein the fan is disposed downstream of the heat exchanger in the flow direction so that outdoor air is suckable via the first connection into the casing and air having passed the heat exchanger is blowable to the outside of the building via the second connection, wherein a centerline in the side view and passing the apex of the V-shaped heat exchanger extends horizontally when the heat exchanger is installed in the building, and a baffle plate is disposed at the apex of the heat exchanger and facing the air flow, the air conditioner being characterized in that the baffle plate has, in the side view, an equiangular triangular shape, wherein the apex of the triangle is located on the centerline of the heat exchanger and facing the air flow. an air duct; and a heat exchanger unit to be disposed inside a building, the heat exchanger unit comprising: a casing having a duct to be flown through by air, a first connection connected to the air duct for communicating the heat exchanger unit with the outside of the building and a second connection connected to the air duct again for leading to the outside of the building, a fan disposed in the casing and configured to induce a flow of the air through the duct in a flow direction, a heat exchanger being V-shaped in side view with an apex at one end and an opening at the opposite end, the heat exchanger being disposed in the duct with the apex directed towards the first connection and facing the air flow, wherein the fan is disposed downstream of the heat exchanger in the flow direction so that outdoor air is suckable via the first connection into the casing and air having passed the heat exchanger is blowable to the outside of the building via the second connection, wherein a centerline in the side view and passing the apex of the V-shaped heat exchanger extends horizontally when the heat exchanger is installed in the building, and a baffle plate is disposed at the apex of the heat exchanger and facing the air flow, the air conditioner being characterized in that the baffle plate has, in the side view, an equiangular triangular shape, wherein the apex of the triangle is located on the centerline of the heat exchanger and facing the air flow. a casing having a duct to be flown through by air, a first connection connected to the air duct for communicating the heat exchanger unit with the outside of the building and a second connection connected to the air duct again for leading to the outside of the building, a fan disposed in the casing and configured to induce a flow of the air through the duct in a flow direction, a heat exchanger being V-shaped in side view with an apex at one end and an opening at the opposite end, the heat exchanger being disposed in the duct with the apex directed towards the first connection and facing the air flow, wherein the fan is disposed downstream of the heat exchanger in the flow direction so that outdoor air is suckable via the first connection into the casing and air having passed the heat exchanger is blowable to the outside of the building via the second connection, wherein a centerline in the side view and passing the apex of the V-shaped heat exchanger extends horizontally when the heat exchanger is installed in the building, and a baffle plate is disposed at the apex of the heat exchanger and facing the air flow, the air conditioner being characterized in that the baffle plate has, in the side view, an equiangular triangular shape, wherein the apex of the triangle is located on the centerline of the heat exchanger and facing the air flow.