Abstract: A construction of a filter 170 that allows air stream from a blower fan 120 to pass through a heat exchanger 130 arranged adjacent to the blower fan 120 after its flowing direction is changed by about 90 degrees. The filter 170 is disposed on the front surface of the heat exchanger on the upstream side of the air flow and has a construction such that airflow resistance of the filter gradually changes with respect to the flow velocity of air passing through the filter and in this way, flow velocity distribution of air passing through the heat exchanger becomes uniform. In this case, a fold pitch P of folds of the filter that is folded or a peak height h of the folds is changed in a plurality of steps or without any steps.