a plurality of water passages allowing flow of water , a plurality of alcohol passages allowing flow of alcohol and a plurality of high temperature gas passages heating the water passages and the alcohol passages are independently provided in a heat exchanging portion . liquid alcohol is supplied from a first header to the alcohol passage and water is supplied from a second header to the water passage . the water passage is preferably adapted to make contact with a high temperature section of the high temperature gas passage and the alcohol passage is preferably adapted to make contact with the low temperature section of the high temperature gas passage . by separately vaporizing water and alcohol in this way , the mixing ratio of the water vapor and alcohol vapor can be controlled with high response .