A condensing type dryer uses a heat exchanger in which condensed water can be smoothly discharged through a water-discharging slot formed in a rear end portion of a rear cover of the heat exchanger. The water-discharging slot prevents an air flowing resistance which can be caused by condensed water pooling at the rear end portion of the rear cover. Also, leakage-preventing walls enhance the heat exchanging function by ensuring a uniform flow of cold external air through the heat changer. The leakage-preventing walls prevent external air from leaking around the lateral edges of the heat exchanger.