A sensor unit comprising a sensor section that includes an element reacting with a gaseous detection target substance and detects the detection target substance, and a holder that internally holds the sensor section and includes an inlet port that introduces a gas into inside of the holder , characterized in that : the sensor section includes a case inside which the element is arranged, and which has a first opening provided in one face , and a second opening provided in another face on an opposite side to the one face ; and the holder includes: a supply port (N1) that is arranged at a position that is close to the one face , and that allows a gas that is introduced into inside of the holder to pass through to the one face side, a hollow section into which a gas having passed through inside of the case flows from the second opening , a first flow channel (R4) having annular or C-shape that is formed in a circumferential direction of the hollow section , a plurality of second flow channels (R7) that are provided at predetermined intervals in the circumferential direction of the hollow section and that connect the hollow section and the first flow channel (R4), and an exhaust port that is connected to the first flow channel (R4) at a different position from the second flow channels (R7) and that discharges a gas that is inside the holder . the sensor section includes a case inside which the element is arranged, and which has a first opening provided in one face , and a second opening provided in another face on an opposite side to the one face ; and the holder includes: a supply port (N1) that is arranged at a position that is close to the one face , and that allows a gas that is introduced into inside of the holder to pass through to the one face side, a hollow section into which a gas having passed through inside of the case flows from the second opening , a first flow channel (R4) having annular or C-shape that is formed in a circumferential direction of the hollow section , a plurality of second flow channels (R7) that are provided at predetermined intervals in the circumferential direction of the hollow section and that connect the hollow section and the first flow channel (R4), and an exhaust port that is connected to the first flow channel (R4) at a different position from the second flow channels (R7) and that discharges a gas that is inside the holder . a supply port (N1) that is arranged at a position that is close to the one face , and that allows a gas that is introduced into inside of the holder to pass through to the one face side, a hollow section into which a gas having passed through inside of the case flows from the second opening , a first flow channel (R4) having annular or C-shape that is formed in a circumferential direction of the hollow section , a plurality of second flow channels (R7) that are provided at predetermined intervals in the circumferential direction of the hollow section and that connect the hollow section and the first flow channel (R4), and an exhaust port that is connected to the first flow channel (R4) at a different position from the second flow channels (R7) and that discharges a gas that is inside the holder . <EOS>