A stick-on deep body thermometer includes a light emitting unit emitting detection light, a first scattering portion scattering the detection light passing a light-transmissive lower exterior body, a first adhesive layer that is adhesive, light-transmissive, and stuck on the lower exterior body, where the detection light scattered by the first scattering portion enters, a second scattering portion scattering detection light propagating in the first adhesive layer, a light receiving unit receiving detection light scattered by the second scattering portion, passing the lower exterior body, and incident thereon, and a contact state determination unit determining the stick-on deep body thermometer and a living body surface are in contact when a light receiving amount of the detection light is under a predetermined value, and determining they are not in contact when the light receiving amount of the detection light is not under the predetermined value.
