PURPOSE: To improve and stabilize the accuracy of a pressure sensor by making the atmosphere side of the sensor not fixed except a sensor case and resin case which are to be fixed.

CONSTITUTION: A pressure detecting path is constituted by sticking a pressure sensor element 1 to the upper surface of the pressure introducing tube 4 of a sensor case 5. The sensor element 1 is electrically connected to leads 8, a lead frame 3, a circuit board 13, and terminals 12. In addition, such an electric circuit as the amplifier circuit, etc., is formed on the circuit board 10 and the surfaces of the sensor case 5 and board 10 are coated with a potting material 11 by housing the case 5 and board 10 in a resin case 6. Then, a resin case B14 is fixed to the resin case 6 after injecting the potting material 11. The sensor case 5 is not fixed to the resin case B14, but kept in a free state. Since the atmosphere side of a pressure detecting device is kept free, no unreasonable force is applied to the element 1 and the sensor element 1 becomes stable against such a thermal stress as the temperature change, etc.