Abstract: Sensing device for canister has canister sensor 40 that detects state of activated carbon 10 filling an inside of casing 11 of the canister. Peripheries of temperature sensing element 51 and current application unit of the canister sensor 40 which are arranged in the casing 11 are covered in non-conductive thick insulating material 54. Root portion 56, which is covered in the insulating material 54, of heat transfer plate 55 having high heat conductivity is arranged with the root portion 56 being adjacent to the temperature sensing element 51, in order to increase sensor sensitivity by increasing heat transfer. Top end portion 57, which protrudes from the insulating material 54, of the heat transfer plate 55 is exposed to the inside of the casing 11. Insulating layer 63 is formed at least on surface of the root portion 56 of the heat transfer plate 55 by surface treatment.