An in-vehicle absorption heat pump device mounted on a vehicle, comprising: a regenerator for heating an absorbent; an in-vehicle heat source for heating the absorbent in the regenerator; a gas-liquid separator for separating gas phase and liquid phase from the absorbent heated by the in-vehicle heat source in the regenerator so as to relatively increase concentration of the absorbent; a condenser for condensing the gas phase separated from the absorbent to form a condensate, the condenser being connected with a gas phase portion in the gas-liquid separator via a passage which extends from a gas phase outlet port of the gas-liquid separator to an inlet port of the condenser; an evaporator for evaporating the condensate condensed in the condenser to form vapor; an absorber for bringing the absorbent in liquid phase relatively concentrated by the separation of the gas phase in the gas-liquid separator in contact with the gas phase evaporated in the evaporator so as to cause the absorbent to absorb the gas phase and be relatively diluted and allow the diluted absorbent to be supplied to the regenerator; an absorbent circulation source for circulating the absorbent in a circulation passage connecting the regenerator, the gas-liquid separator and the absorber; a bypass passage connecting a liquid-phase storing portion of the gas-liquid separator and the regenerator while bypassing the absorber; and a bypass transfer source provided in the bypass passage, transferring the absorbent in liquid phase stored in the gas-liquid separator and returning the absorbent stored in the gas-liquid separator to the regenerator while bypassing the absorber, characterized in that: the regenerator is provided in a vehicle external space below a partition wall for vertically separating an engine room above and the vehicle external space below, and accordingly located below the gas-liquid separator, the condenser, the evaporator and the absorber, which are provided above the partition wall. a regenerator for heating an absorbent; an in-vehicle heat source for heating the absorbent in the regenerator; a gas-liquid separator for separating gas phase and liquid phase from the absorbent heated by the in-vehicle heat source in the regenerator so as to relatively increase concentration of the absorbent; a condenser for condensing the gas phase separated from the absorbent to form a condensate, the condenser being connected with a gas phase portion in the gas-liquid separator via a passage which extends from a gas phase outlet port of the gas-liquid separator to an inlet port of the condenser; an evaporator for evaporating the condensate condensed in the condenser to form vapor; an absorber for bringing the absorbent in liquid phase relatively concentrated by the separation of the gas phase in the gas-liquid separator in contact with the gas phase evaporated in the evaporator so as to cause the absorbent to absorb the gas phase and be relatively diluted and allow the diluted absorbent to be supplied to the regenerator; an absorbent circulation source for circulating the absorbent in a circulation passage connecting the regenerator, the gas-liquid separator and the absorber; a bypass passage connecting a liquid-phase storing portion of the gas-liquid separator and the regenerator while bypassing the absorber; and a bypass transfer source provided in the bypass passage, transferring the absorbent in liquid phase stored in the gas-liquid separator and returning the absorbent stored in the gas-liquid separator to the regenerator while bypassing the absorber, characterized in that: the regenerator is provided in a vehicle external space below a partition wall for vertically separating an engine room above and the vehicle external space below, and accordingly located below the gas-liquid separator, the condenser, the evaporator and the absorber, which are provided above the partition wall.