A pressure sensor includes a connector case having a recess, in which a sensor chip is contained and an oil is filled. The recess filled with the oil is sealed by a metal diaphragm. The sensor chip for outputting signals and the circuit chip having a processing circuit for processing the signals from the sensor chip, are stacked. That is, the circuit chip is provided between a bottom wall surface of the recess and the sensor chip. The processing circuit is covered by at least a part of the sensor chip, and the processing circuit of the circuit chip is arranged at a place where the processing circuit can avoid contact with the oil. Because the processing circuit of the circuit chip is not exposed to the oil, the processing circuit can be effectively restricted from being charged due to a polarization of the oil.