A pipe erroneous assembly preventing structure comprising: a pipe; and a case provided with a pipe insertion hole into which the pipe is inserted on a case wall surface thereof, wherein the pipe is provided with a stay (11, 12) in which a stay-side abutting portion extending in a direction orthogonal to an axial center of the pipe and a stay claw portion extending from the stay-side abutting portion along an insertion direction intersect with each other in an L shape, the case is provided with: a hole forming portion surrounding a peripheral of the pipe insertion hole; a first protrusion portion provided in the hole forming portion; a case-side abutting portion (24, 25) which is recessed in the first protrusion portion and to which the stay-side abutting portion of the stay (11, 12) abuts when the pipe is correctly inserted into the pipe insertion hole; and a second protrusion portion protruding from the case wall surface and provided on an outside of the hole forming portion at a position different from the case-side abutting portion (24, 25) in a circumferential direction, and a length of the stay claw portion in the insertion direction is set to Ls, a distance from the case wall surface to the case-side abutting portion (24, 25) is set to Lg, and a distance from the case wall surface to the second protrusion portion is set to Lp, wherein Lg-Lp < Ls ≤ Lg is satisfied. a pipe; and a case provided with a pipe insertion hole into which the pipe is inserted on a case wall surface thereof, wherein the pipe is provided with a stay (11, 12) in which a stay-side abutting portion extending in a direction orthogonal to an axial center of the pipe and a stay claw portion extending from the stay-side abutting portion along an insertion direction intersect with each other in an L shape, the case is provided with: a hole forming portion surrounding a peripheral of the pipe insertion hole; a first protrusion portion provided in the hole forming portion; a case-side abutting portion (24, 25) which is recessed in the first protrusion portion and to which the stay-side abutting portion of the stay (11, 12) abuts when the pipe is correctly inserted into the pipe insertion hole; and a second protrusion portion protruding from the case wall surface and provided on an outside of the hole forming portion at a position different from the case-side abutting portion (24, 25) in a circumferential direction, and a hole forming portion surrounding a peripheral of the pipe insertion hole; a first protrusion portion provided in the hole forming portion; a case-side abutting portion (24, 25) which is recessed in the first protrusion portion and to which the stay-side abutting portion of the stay (11, 12) abuts when the pipe is correctly inserted into the pipe insertion hole; and a second protrusion portion protruding from the case wall surface and provided on an outside of the hole forming portion at a position different from the case-side abutting portion (24, 25) in a circumferential direction, and a length of the stay claw portion in the insertion direction is set to Ls, a distance from the case wall surface to the case-side abutting portion (24, 25) is set to Lg, and a distance from the case wall surface to the second protrusion portion is set to Lp, wherein Lg-Lp < Ls ≤ Lg is satisfied.