A temperature measuring device of a power semiconductor apparatus that accurately detects chip temperature even where a gradient of the measured characteristic line segment is different from a designed gradient, including a chip temperature detecting circuit that includes an A/D converter delivering a measurement value of a digital converted forward voltage across a temperature detecting diode and an operational processing unit for calibration and chip temperature calculation. In calibration processing, different known reference voltages are applied by a reference connected in place of the diode and a gradient of the line segment connecting the measurement values is calculated. The gradient is stored in a memory with an offset correction value that is one of the measurement values. A chip temperature is calculated based on a forward voltage across the diode calculated based on the measurement value and the stored values of the gradient and the offset correction value.