A ring type heat flow measuring apparatus has a heat receiving section that comes into contact with a measurement target and receives heat and releases heat through transferring from a first heat diffusing member, a heat transfer layer, a second heat diffusing member, and a heat releasing section in this order. A first temperature sensor measures a temperature of the first heat diffusing member, a second temperature sensor measures a temperature of the second heat diffusing member, and heat flow is calculated using these temperatures. Heat diffusing effects of the first heat diffusing member and the second heat diffusing member enable highly accurate temperature measurement to be stably performed regardless of relative positions between an arterial blood vessel as a heat source and the first temperature sensor and the second temperature sensor.
