To solve the following problem: reliability is gradually deteriorated since a detection value by a glow plug-integrated cylinder internal pressure sensor is changed with time in association with adhesion and accumulation of deposits.

In this device for calibrating the glow plug-integrated cylinder internal pressure sensor 20, the pressure receiving portion of a cylinder internal pressure sensor 20a for detecting pressure in the combustion chamber 12 of an engine 10 doubles as the heating portion of a glow plug 20b. The device includes: a storage section 40 storing an initial value of cylinder internal pressure Pn detected by the glow plug-integrated cylinder internal pressure sensor 20 when the engine is in a predetermined operating condition as reference cylinder internal pressure PR; an operating condition determination section 35 determining whether or not the engine 10 is in the predetermined operating condition; a correction coefficient setting section 41 calculating a difference P between the detected cylinder internal pressure Pn and the reference cylinder internal pressure PR and setting a correction coefficient for correcting the cylinder internal pressure Pn based on the difference P, when the engine 10 is in the predetermined operating condition; and a cylinder internal pressure correction section 42 correcting the cylinder inner pressure by multiplying the detected cylinder inner pressure Pn by the set correction coefficient .