A core body thermometer includes a substrate, a heat receiving terminal with which heat from a subject is received and which divides the heat into first heat flow and second heat flow and causes the first heat flow and the second heat flow to flow out, a first heat flow measurement system that measures the first heat flow using a first input-side temperature sensor and a first output-side temperature sensor, a second heat flow measurement system that measures the second heat flow using a second input-side temperature sensor and a second output-side temperature sensor, a first thermal resistance body provided between the heat receiving terminal and the first input-side temperature sensor, and a second thermal resistance body provided between the heat receiving terminal and the second input-side temperature sensor.
