Temperature rises of all parts of gear equipment and oil must be known when the bulk temperature rise of gears is calculated. Though there is a thermal network method which can be used to predict temperature rises in gears, the true state is more complicated and the temperature rise of oil has not been discussed. In the present paper, the heat quantity at no load, the heat release coefficient of the gearbox and the quantity entering the gear axis from the bearing are calculated with experimental data, and the temperature rises of the gear surfaces and oils are measured. A method of calculating temperature rises of all parts of gear equipment and of oil is proposed. The predicted results are compared with the measured values. The contribution of the heat entering the gear equipment and the heat escaping from the gear equipment are calculated based on the predicted results.