To provide a Brayton cycle engine capable of improving efficiency in regenerating exhaust heat without disposing a regenerator, and advantageous for miniaturization and integration.

A Brayton cycle engine 1 having a plurality of screw rotors 3-5 disposed in a casing 2, further includes a reference screw rotor 3, a compression screw rotor 4 rotated while engaged with the reference screw rotor 3 so that a working medium is carried while compressed, and an expansion screw rotor 5 rotated while engaged with the reference screw rotor 3 so that a working medium is carried while expanding. A part of the reference screw rotor 3 configures a heat exchanging portion T for allowing the working medium compressed in the compression screw rotor 4 to exchange heat with the working medium expanding in the expansion screw rotor 5.