A jet engine comprising: an inlet configured to introduce air; and a combustor having a fuel injection port from which a fuel can be injected and configured to combust the fuel injected from the fuel injection port by using the air introduced from the inlet, wherein the combustor comprises a separation section defining an air passage, through which the air introduced from the inlet flows, between a downstream end of the inlet in the flow direction of the air and the fuel injection port, characterized in that: a plurality of turbulent flow generating sections (20;25) are arranged in the separation section to make the air flow in the air passage turbulent, and wherein each of the plurality of turbulent flow generating sections (20;25) comprises a member (21;22;25A,25B) that can create the turbulence in a boundary layer of the air flow on a wall surface of the separation section as it protrudes from the wall surface towards the air passage, and that can restrain the turbulence in the boundary layer of the air flow a) by moving from the position protruding from the wall surface of the separation section to a position not protruding from the wall surface or along the wall surface of the separation section, or b) by disappearing. an inlet configured to introduce air; and a combustor having a fuel injection port from which a fuel can be injected and configured to combust the fuel injected from the fuel injection port by using the air introduced from the inlet, wherein the combustor comprises a separation section defining an air passage, through which the air introduced from the inlet flows, between a downstream end of the inlet in the flow direction of the air and the fuel injection port, characterized in that: a plurality of turbulent flow generating sections (20;25) are arranged in the separation section to make the air flow in the air passage turbulent, and wherein each of the plurality of turbulent flow generating sections (20;25) comprises a member (21;22;25A,25B) that can create the turbulence in a boundary layer of the air flow on a wall surface of the separation section as it protrudes from the wall surface towards the air passage, and that can restrain the turbulence in the boundary layer of the air flow a) by moving from the position protruding from the wall surface of the separation section to a position not protruding from the wall surface or along the wall surface of the separation section, or b) by disappearing. a plurality of turbulent flow generating sections (20;25) are arranged in the separation section to make the air flow in the air passage turbulent, and wherein each of the plurality of turbulent flow generating sections (20;25) comprises a member (21;22;25A,25B) that can create the turbulence in a boundary layer of the air flow on a wall surface of the separation section as it protrudes from the wall surface towards the air passage, and that can restrain the turbulence in the boundary layer of the air flow a) by moving from the position protruding from the wall surface of the separation section to a position not protruding from the wall surface or along the wall surface of the separation section, or b) by disappearing. a) by moving from the position protruding from the wall surface of the separation section to a position not protruding from the wall surface or along the wall surface of the separation section, or b) by disappearing.