In a combustion pressure sensor having built-in charge amplifier, signal line overheating and deterioration of detection accuracy is restricted. The combustion pressure sensor includes a sensor body that includes a piezoelectric element having one end connected to chassis ground through a housing and detects pressure in a combustion chamber of engine, and a charge amplifier that includes at least a voltage converting unit converting output of the sensor body into voltage signal and a reference voltage generating unit generating reference voltage supplied to the voltage converting unit and operates on power supplied from a signal processing unit disposed outside. The reference voltage generating unit includes a voltage generating circuit having a constant current circuit and a resistor connected in series. The voltage generating circuit has one end connected to power line extending from the signal processing unit, and the other end connected to the end of the piezoelectric element.