An acid gas removal apparatus of one embodiment includes: an absorption tower bringing gas containing acid gas into contact with an acid gas absorbent of a solution containing a thermosensitive nitrogen-containing compound (formula (1)) and having LCST at a predetermined temperature to absorb the acid gas into the absorbent and remove the acid gas from the gas; a first heater heating the absorbent to LCST of the solution or more; a tank phase-separating the absorbent into a rich absorbent phase and a lean absorbent phase whose content of the thermosensitive compound is higher; a second heater heating the rich phase; a regeneration tower releasing the acid gas in the rich phase; a third heater provided at the regeneration tower heating the rich phase.
