An air conditioner comprising: a housing having an inlet and an outlet, the outlet comprising first and second guide surfaces (14, 15) that face each other; a heat exchanger configured to heat-exchange air suctioned through the inlet; a blower fan configured to suction air from the inlet, to pass air through the heat exchanger, and to discharge air toward the outlet; and an airflow control unit comprising: a guide member (101, 201) provided on the first guide surface or the second guide surface to extend from a central portion of the outlet along a width direction of the outlet, an airflow control driving source (102, 202) including a pinion gear and configured to generate power to move the guide member (101, 201), and a transmission member including a rack gear configured to engage the pinion gear to connect the guide member (101, 201) to the airflow control driving source (102, 202) and thereby transmit the power generated by the airflow control driving source (102, 202) to the guide member (101, 201); wherein the guide member (101, 201) is configured to move: in an upward direction along the first guide surface or the second guide surface between a first position adjacent to an end portion of the outlet from which air is discharged and a second position spaced further from the end portion of the outlet when the pinion gear of the airflow control driving source (102, 202) is rotated clockwise, and in a downward direction along the first guide surface or the second guide surface between the second position and the first position when the pinion gear of the airflow control driving source (102, 202) is rotated anticlockwise. a housing having an inlet and an outlet, the outlet comprising first and second guide surfaces (14, 15) that face each other; a heat exchanger configured to heat-exchange air suctioned through the inlet; a blower fan configured to suction air from the inlet, to pass air through the heat exchanger, and to discharge air toward the outlet; and an airflow control unit comprising: a guide member (101, 201) provided on the first guide surface or the second guide surface to extend from a central portion of the outlet along a width direction of the outlet, an airflow control driving source (102, 202) including a pinion gear and configured to generate power to move the guide member (101, 201), and a transmission member including a rack gear configured to engage the pinion gear to connect the guide member (101, 201) to the airflow control driving source (102, 202) and thereby transmit the power generated by the airflow control driving source (102, 202) to the guide member (101, 201); a guide member (101, 201) provided on the first guide surface or the second guide surface to extend from a central portion of the outlet along a width direction of the outlet, an airflow control driving source (102, 202) including a pinion gear and configured to generate power to move the guide member (101, 201), and a transmission member including a rack gear configured to engage the pinion gear to connect the guide member (101, 201) to the airflow control driving source (102, 202) and thereby transmit the power generated by the airflow control driving source (102, 202) to the guide member (101, 201); wherein the guide member (101, 201) is configured to move: in an upward direction along the first guide surface or the second guide surface between a first position adjacent to an end portion of the outlet from which air is discharged and a second position spaced further from the end portion of the outlet when the pinion gear of the airflow control driving source (102, 202) is rotated clockwise, and in a downward direction along the first guide surface or the second guide surface between the second position and the first position when the pinion gear of the airflow control driving source (102, 202) is rotated anticlockwise. in an upward direction along the first guide surface or the second guide surface between a first position adjacent to an end portion of the outlet from which air is discharged and a second position spaced further from the end portion of the outlet when the pinion gear of the airflow control driving source (102, 202) is rotated clockwise, and in a downward direction along the first guide surface or the second guide surface between the second position and the first position when the pinion gear of the airflow control driving source (102, 202) is rotated anticlockwise.