To provide a heat exchanger for an aircraft hardly causing a crack and having high reliability by providing a compact and lightweight thermal expansion absorbing means of simple structure.

This heat exchanger 40 for the aircraft includes: a thermally conductive core 60 having high temperature channels 66 connecting an inlet 63 on the side of a high temperature to an outlet 64 on the side of a high temperature and low temperature channels 65 connecting an inlet 61 on the side of a low temperature to an outlet 62 on the side of a low temperature; ducts 31 on the side of a high temperature, connected between pipes 72 on the side of a high temperature circulating engine bleed air 4 led from the engine 1 of the aircraft; and ducts 30 on the side of a low temperature, connected between pipes 71 on the side of a low temperature circulating ram air 5 or engine fan air 6. The high temperature channels 66 are arranged between the ducts 31 on the side of the high temperature, and the low temperature channel 65 are arranged between the ducts 31 on the side of the low temperature. At least one of the inlet 61 on the side of the low temperature and the outlet 62 on the side of the low temperature is connected to the ducts 30 on the side of the low temperature through bellows 41.