To obtain measuring data effective to thin an aluminum can and correctly determine a proper operation of a sterilization device based on the measuring data, by providing a can internal pressure-measuring part and a boiler internal pressure- measuring part, and calculating a differential pressure between a pressure in a can and a pressure in a boiler.

A can internal pressure-measuring unit 12 is stored and protected within a heatproof and pressure-resistant container. An internal pressure of canned food and an internal pressure of a boiler can be correctly and continuously measured at the same time. The measured pressure is corrected by a correcting part 29 based on a temperature in the heatproof and pressure-resistant container. A pressure inside a can, a temperature inside the can and the pressure in the boiler stored in a memory part 26 are separately distinguished and read into a computer. A graph of pressure changes in a sample can A and the boiler is obtained by processing measuring data. A can temperature-measuring part 25 measuring a temperature in a second sample can B processes the same way and obtains a graph of temperature changes. Whether a sterilization treatment is properly carried out or not is detected from a holding state of the temperature in the canned food, and a tolerance of the can is detected from a differential pressure between the pressure in the can and the pressure in the boiler.