There is provided an evaporator (23) disposed between an exhaust manifold (22) and an exhaust pipe (24), the evaporator (23) including, in sequence from the upstream side toward the downstream side, a first exhaust gas passage (56) having a third stage heat exchanger (H3), a second exhaust gas passage (55) having a second stage heat exchanger (H2), and a third exhaust gas passage (50) having a first stage heat exchanger (H1). Formed in the annular second exhaust gas passage (55) of the second stage heat exchanger (H2) is a spiral passage divided by a spiral heat transfer plate (68), and arranged in a spiral shape so as to follow the heat transfer plate (68) are a plurality of undulating heat transfer tubes (67) that are stacked out of phase. Increasing the exhaust gas passage length by the heat transfer plate (68) and agitating the flow of exhaust gas by the heat transfer tubes (67) enables the opportunity for contact of the exhaust gas with the heat transfer plate (68) and the heat transfer tubes (67) to be increased, thereby enhancing the heat exchange efficiency.