To measure an internal pressure of a can of canned food at an optional point in a retort boiler, etc., by uniting a needle in one body with the can by a holder and introducing the internal pressure of the can to a sensor part via the needle inserted into the can.

A hold part 31 clamps and holds a trunk part of a can of canned food from an outer periphery of the can. A hollow needle 27 is projected/ retreated to the center of the can from an inner face of the hold part 31. A predetermined area between an outer face of the can in the periphery of the needle 27 and the inner face of the hold part 31 is maintained in an airtight state by a shield part 37. A sensor connected to the needle 27 converts an internal pressure of the can to an electric signal. The electric signal from the sensor is taken out via a signal line outside a can-heating/treating device. The sensor is accommodated inside a main body part 3 holding airtight and heat-insulating properties, and therefore not, easily influenced by an external temperature or humidity, etc. Measuring results are accordingly correct.