An air conditioner includes a housing (1) provided with one or more air suction openings (2) and one or more air discharge openings (3); a cross flow fan (4) disposed in the housing (1); and a fin attached heat exchanger unit (5) disposed between the air suction openings and the cross flow fan and having a front heat exchanger (5a), where a coolant tube (7) is arranged in a lower portion of the front heat exchanger (5a) in a single row and in an upper portion thereof in two rows; and a rear heat exchanger (5b), where the coolant tube is arranged in two rows, the front and rear heat exchanger being coupled in a substantially inverted "V" shape. A fin (8) of the front heat exchanger is provided with a slit (9a) at a joint portion of the lower and upper portion thereof and a protrusion is formed at the slit to interfere with a suction air flow.