A sensing device is provided. The sensing device includes a plurality of infrared thermosensitive elements and a plurality of resistor-capacitor (RC) oscillators. The plurality of infrared thermosensitive elements are arranged in an array. Each of the plurality of infrared thermosensitive elements has a resistance value which changes with a temperature of the infrared thermosensitive element by absorbing infrared radiation and generates a sensing voltage corresponding to the resistance value. The plurality of RC oscillators are coupled to the plurality of infrared thermosensitive elements to receive the corresponding sensing values, respectively. Each of the plurality of RC oscillators generates a digital sensing signal according to the corresponding sensing value to indicate the temperature of the corresponding infrared thermosensitive element. Each of the plurality of RC oscillators is disposed under the corresponding infrared thermosensitive element.