To provide a highly reliable and accurate pressure sensor in which a sensor chip is protected against damage and whose characteristics are prevented from deteriorating.

When the upper and lower cases 11, 12 of the sensor 10 are jointed at the abutting faces 11a, 12a, the upper case 11 is provided with a through hole A1 extending from the abutting face 11a to the opposing face while the lower case 12 is provided with a through hole B2 extending vertically from the abutting face 12a of the lower case 12 to the bottom face 12b. Furthermore, a through hole C3 extending from the bottom of the lower case 12 and opening to the side face is also provided. The through holes A1, B2 extending from the upper surface of the upper case 11 to the lower surface of the lowercase 12 are then coupled each other to communicate with the through hole C3. A through hole D4 extending into the lower case 12 is also provided and a sensor chip 13 is arranged thereon and then a reference pressure is introduced through the through hole D4.