To provide a thermoelectric generator which prevents breakage of a thermoelectric conversion module due to heat damage and increases a power generation amount of the thermoelectric conversion module.

A communication hole 47 allows a downstream side inner pipe 24 forming a main passage 25 to communicate with an outer pipe 22 forming a sub passage 28. Further, a communication hole 48a allows the downstream side inner pipe 24 located at the downstream side relative to the communication hole 47 to communicate with the outer pipe 22, and a diameter-reduced part 23a is formed at an upstream side inner pipe 23 located at the upstream side relative to the communication hole 47. Further, a thermoelectric conversion module 30 having a high operation temperature range is provided between an upstream part of the downstream side inner pipe 24 and an upstream part of a coolant pipe 29, and a thermoelectric conversion module 38 having a low operation temperature range is provided between a downstream part of the downstream side inner pipe 24 and a downstream part of the coolant pipe 29.