A thermoelectric generator arranged in an outdoor atmosphere whose temperature changes periodically in day and night so as to generate electricity by using the change of temperature of the outdoor atmosphere, the thermoelectric generator comprising: a thermal conductor contacting with the outdoor atmosphere to conduct thermal exchange with the outdoor atmosphere; a thermal accumulator; and at least one pair of a thermoelectric conversion unit and a thermal resistor, the pair of the thermoelectric conversion unit and the thermal resistor being arranged between the thermal conductor and the thermal accumulator, wherein the thermal resistor and the associated thermoelectric conversion unit contact with each other at one sides thereof, and the other side of one of the pair of the thermal resistor and the associated thermoelectric conversion unit contacts with the thermal conductor, while the other side of the other of the pair of the thermal resistor and the associated thermoelectric conversion unit contacts with the thermal accumulator, and the thermal accumulator is covered by a covering layer except the area thereof contacting with the thermoelectric conversion unit and the thermal resistor, the covering layer having a thermal insulating property, characterised by the thermal resistance of the thermal resistor is determined based on a thermal time constant, the thermal time constant being defined as a numerical value which is calculated by multiplying the thermal capacity of the thermal accumulator by the total thermal resistance of a thermal network composed of the thermal conductor, the thermal resistor, the thermoelectric conversion unit and the thermal accumulator, the thermal time constant being determined in such a way that a definite delay is caused between a repetition cycle of ups and downs of the temperature of the outdoor atmosphere and a repetition cycle of ups and downs of the temperature of the thermal accumulator so as to effect the temperature difference required for electric generation between the thermal conductor and the thermal accumulator, wherein electric energy is generated from the thermoelectric conversion unit by the temperature difference caused between the thermal conductor and the thermal accumulator. a thermal conductor contacting with the outdoor atmosphere to conduct thermal exchange with the outdoor atmosphere; a thermal accumulator; and at least one pair of a thermoelectric conversion unit and a thermal resistor, the pair of the thermoelectric conversion unit and the thermal resistor being arranged between the thermal conductor and the thermal accumulator, wherein the thermal resistor and the associated thermoelectric conversion unit contact with each other at one sides thereof, and the other side of one of the pair of the thermal resistor and the associated thermoelectric conversion unit contacts with the thermal conductor, while the other side of the other of the pair of the thermal resistor and the associated thermoelectric conversion unit contacts with the thermal accumulator, and the thermal accumulator is covered by a covering layer except the area thereof contacting with the thermoelectric conversion unit and the thermal resistor, the covering layer having a thermal insulating property, characterised by the thermal resistance of the thermal resistor is determined based on a thermal time constant, the thermal time constant being defined as a numerical value which is calculated by multiplying the thermal capacity of the thermal accumulator by the total thermal resistance of a thermal network composed of the thermal conductor, the thermal resistor, the thermoelectric conversion unit and the thermal accumulator, the thermal time constant being determined in such a way that a definite delay is caused between a repetition cycle of ups and downs of the temperature of the outdoor atmosphere and a repetition cycle of ups and downs of the temperature of the thermal accumulator so as to effect the temperature difference required for electric generation between the thermal conductor and the thermal accumulator, wherein electric energy is generated from the thermoelectric conversion unit by the temperature difference caused between the thermal conductor and the thermal accumulator.