A physical quantity detection device that is configured to detect a plurality of physical quantities of a measuring target gas flowing in a main passage, comprising: a housing that is configured to be disposed in the main passage; a printed circuit board that is formed to be inserted in the housing; a plurality of detection sensors (452, 453, 454, 455, 456) that are mounted on one surface and the other surface of the printed circuit board; and a first bypass passage through which the measuring target gas is taken in from a first bypass passage inlet opened to the housing, and the measuring target gas is discharged from a first bypass passage outlet opened to the housing; wherein at least one detection sensor among the plurality of detection sensors (452, 453, 454, 455, 456) is disposed in the first bypass passage, and wherein the printed circuit board includes a detection sensor surface region in one surface of the printed circuit board in which the detection sensor is disposed, and a circuit component surface region in which circuit components other than the detection sensor are disposed, wherein a facing surface region is provided in the other surface of the printed circuit board to face the circuit component surface region; characterized in that it further comprises a second bypass passage through which the measuring target gas is taken in from a second bypass passage inlet opened to the housing, and the measuring target gas is discharged from a second bypass passage outlet opened to the housing, wherein at least one detection sensor different from the detection sensor disposed in the first bypass passage is disposed in the second bypass passage, and in that at least a part of the facing surface region among the other surface of the printed circuit board is exposed to the second bypass passage. a housing that is configured to be disposed in the main passage; a printed circuit board that is formed to be inserted in the housing; a plurality of detection sensors (452, 453, 454, 455, 456) that are mounted on one surface and the other surface of the printed circuit board; and a first bypass passage through which the measuring target gas is taken in from a first bypass passage inlet opened to the housing, and the measuring target gas is discharged from a first bypass passage outlet opened to the housing; wherein at least one detection sensor among the plurality of detection sensors (452, 453, 454, 455, 456) is disposed in the first bypass passage, and wherein the printed circuit board includes a detection sensor surface region in one surface of the printed circuit board in which the detection sensor is disposed, and a circuit component surface region in which circuit components other than the detection sensor are disposed, wherein a facing surface region is provided in the other surface of the printed circuit board to face the circuit component surface region; characterized in that it further comprises a second bypass passage through which the measuring target gas is taken in from a second bypass passage inlet opened to the housing, and the measuring target gas is discharged from a second bypass passage outlet opened to the housing, wherein at least one detection sensor different from the detection sensor disposed in the first bypass passage is disposed in the second bypass passage, and in that at least a part of the facing surface region among the other surface of the printed circuit board is exposed to the second bypass passage.