A seating detection device includes: a first seating sensor (20R, 20L), installed in each of opposite ends of seats (11 R, 11C, 11 L) arranged side by side in a rear seat row in a vehicle and located in a seating surface portion (12R, 12C, 12L) of the corresponding seat; and first load detection switches (C1, C2, C3, C4), installed in the first seating sensor to be brought into a conducting state when a load is applied thereto and arranged side by side in the vehicle width direction, wherein two adjacent first load detection switches installed at any one side of a first reference line (Ia) are connected in series, and two adjacent first load detection switches connected in parallel and arranged with the first reference line being interposed therebetween, and two first load detection switches connected in parallel and installed at opposite ends, are connected in series.