A sensing device that adsorbs a substance to be sensed as a gas to a piezoelectric resonator, changes a temperature of the piezoelectric resonator to desorb the substance to be sensed, and senses the substance to be sensed based on a relationship between a change of an oscillation frequency of the piezoelectric resonator and the temperature, the sensing device comprising: a substrate that holds the piezoelectric resonator and a temperature detector to detect a temperature of the crystal resonator; a thermoelectric element unit, disposed at a position in contact with the substrate to change the temperature of the piezoelectric resonator; a support plate that supports the thermoelectric element unit from an opposite side of the position in contact with the substrate; a base portion to which the support plate is secured such that a surface on an opposite side of the surface to support the thermoelectric element unit is in contact with the base portion, the base portion performing at least one of heat supply and heat dissipation to the thermoelectric element unit via the support plate; a housing space included in the base portion that houses a circuit board including integrated circuits which include an oscillator circuit to oscillate the piezoelectric resonator; sockets as electrodes connected to the integrated circuits respectively; and pins as rod-shaped conductive members, removably disposed between electrodes connected to the piezoelectric resonator or the temperature detector and each of the sockets respectively, wherein the substrate, the thermoelectric element unit, and the support plate are integrated to form a sensing module unit removable from the base portion; and, wherein the pins are able to switch, by being inserted into and pulled out from the sockets, electrical connection and disconnection between the piezoelectric resonator and the temperature detector on the substrate, and the integrated circuits in the base portion. a substrate that holds the piezoelectric resonator and a temperature detector to detect a temperature of the crystal resonator; a thermoelectric element unit, disposed at a position in contact with the substrate to change the temperature of the piezoelectric resonator; a support plate that supports the thermoelectric element unit from an opposite side of the position in contact with the substrate; a base portion to which the support plate is secured such that a surface on an opposite side of the surface to support the thermoelectric element unit is in contact with the base portion, the base portion performing at least one of heat supply and heat dissipation to the thermoelectric element unit via the support plate; a housing space included in the base portion that houses a circuit board including integrated circuits which include an oscillator circuit to oscillate the piezoelectric resonator; sockets as electrodes connected to the integrated circuits respectively; and pins as rod-shaped conductive members, removably disposed between electrodes connected to the piezoelectric resonator or the temperature detector and each of the sockets respectively, wherein the substrate, the thermoelectric element unit, and the support plate are integrated to form a sensing module unit removable from the base portion; and, wherein the pins are able to switch, by being inserted into and pulled out from the sockets, electrical connection and disconnection between the piezoelectric resonator and the temperature detector on the substrate, and the integrated circuits in the base portion.