To provide a diaphragm type pressure sensor, capable of surely introducing atmospheric pressure into an atmospheric pressure introducing port of a sensor chip and is capable of surely attaining water-proofness by a molded case body.

This diaphragm type pressure sensor is constituted of a header formed with an oil storage chamber; a diaphragm capable of covering the oil storage chamber of the header; an adapter formed with a pressure receiving chamber capable of covering the diaphragm; an atmosphere-opened pipe provided to receive the atmospheric pressure by the sensor chip attached to the header, with the case body being molded to cover a portion, excluding the tip part of the atmosphere-opened pipe, the header and the adapter; a waterproof recess formed in an atmosphere-opened pipe portion of the case body and having the bottom face lower than the tip part of the atmosphere-opened pipe; and an air inlet groove formed to introduce air into the waterproof recess.