An output device for a heat flow sensor, comprising: an offset value calculation part configured to calculate an offset value for each gain magnification from a plurality of gain magnifications (GM1, GM2, GM3, GM4); an amplification part configured to amplify an output value of the heat flow sensor by a first gain magnification among the plurality of gain magnifications (GM1, GM2, GM3, GM4); an offset part configured to subtract the offset value corresponding to the first gain magnification from the amplified output value; an A/D converter configured to convert the amplified output value after subtraction of the offset value thereof into a digital value; and a gain magnification changing part configured to change the first gain magnification to a further gain magnification among the plurality of gain magnifications (GM1, GM2, GM3, GM4) based on the digital value, characterised in that the gain magnification changing part is configured to change the first gain magnification to a first further gain magnification which is a gain magnification larger than the first gain magnification and closest thereto among the plurality of gain magnifications (GM1, GM2, GM3, GM4), when a maximum value of a plurality of the digital values converted by the A/D converter is less than a lower limit value corresponding to the first gain magnification; and the gain magnification changing part is configured to change the first gain magnification to a second further gain magnification which is a gain magnification smaller than the first gain magnification and closest thereto among the plurality of gain magnifications (GM1, GM2, GM3, GM4), when the digital value is larger than an upper limit value corresponding to the first gain magnification. an offset value calculation part configured to calculate an offset value for each gain magnification from a plurality of gain magnifications (GM1, GM2, GM3, GM4); an amplification part configured to amplify an output value of the heat flow sensor by a first gain magnification among the plurality of gain magnifications (GM1, GM2, GM3, GM4); an offset part configured to subtract the offset value corresponding to the first gain magnification from the amplified output value; an A/D converter configured to convert the amplified output value after subtraction of the offset value thereof into a digital value; and a gain magnification changing part configured to change the first gain magnification to a further gain magnification among the plurality of gain magnifications (GM1, GM2, GM3, GM4) based on the digital value, characterised in that the gain magnification changing part is configured to change the first gain magnification to a first further gain magnification which is a gain magnification larger than the first gain magnification and closest thereto among the plurality of gain magnifications (GM1, GM2, GM3, GM4), when a maximum value of a plurality of the digital values converted by the A/D converter is less than a lower limit value corresponding to the first gain magnification; and the gain magnification changing part is configured to change the first gain magnification to a second further gain magnification which is a gain magnification smaller than the first gain magnification and closest thereto among the plurality of gain magnifications (GM1, GM2, GM3, GM4), when the digital value is larger than an upper limit value corresponding to the first gain magnification.