A water content detection sensor includes a circuit member in which low resistance conductors 1,2 disposed in parallel to each other and a high resistance conductor 3 connecting end portions of the respective low resistance conductors, a carrier body 4 having a water-proof property and an insulating property, and a coating body 5 having a water-proof property and an insulating property, the circuit portion being disposed between the carrier body and the coating body. A plurality of exposure holes 6 are formed to the carrier body or the coating body so as to expose the low resistance conductors at plural portions, and when water content adheres between the exposure holes and the low resistance conductors are then short-circuited in a current conduction state, a current value is made larger than that before the adhesion of the water content. When a small current passes, it is judged that the circuit is normal, and on the other hand, a large current passes, it is judged that water is generated.