A vertically extending air intake duct on a rear of a cab in a delivery vehicle to take in ambient air for an engine through an air intake has a duct body as an outer shell with the air intake on an upper portion; a side branch section on a lower portion of the body and having upper and lower ends opened in the body and outside, respectively; a mesh member extending over the air intake to collect rainwater; a louver for covering the mesh member and the air intake to prevent intrusion of matter other than ambient air; and a drip channel or bead on an inner wall of the duct body and just below the mesh member to capture and guide rainwater flowing down on the inner wall to the upper end of the side branch section.