To provide a heat exchanger whose inside is washed without polluting an atmosphere in a kiln.

This heat exchanger 50 exchanges heat between hot exhaust gas from a substrate kiln for performing baking processing of a glass substrate and supply gas to the substrate kiln. A plurality of heat transfer tubes 61 are installed in the vertical direction by opening the upper-lower ends in a body part 60. The hot exhaust gas from the substrate kiln flows upward from below on the inside of the heat transfer tubes 61 by flowing in from an exhaust inlet port 81, and is exhausted from an exhaust outlet port 71. While, gas newly supplied to the substrate kiln flows downward from above along a clearance between the heat transfer tubes 61 by being taken in from a supply air inlet window 65 of the body part 60, and is sent out to the substrate kiln from a supply air outlet port 64. An organic substance sticking to the inside of the heat transfer tubes 61 is washed by a cleaning liquid delivered from a rinse nozzle 72, and its cleaning liquid is recovered by a liquid receiving part 82.