PURPOSE: To indicate that the pressure of an object to be sensed is above the prescribed value by swing a pointer of an oil pressure gauge significatly when the pressure thereof exceeds the value with the resistance value of a sensor for an automobile varying greatly when closing the prescribed value.

CONSTITUTION: When the oil pressure is low, a substrate 29 is tilted back to incline movable levers 26 and 27 backward to bring the lever 27 into contact with a terminal 35 of a warning lamp 24, causing the lamp 34 to light. As the pressure rises, an engine oil coming from a pressure introduction path pushes a diaphragm and the substrate 29 is pushed up with a push pin 23 to turn forward while the movable levers 26 and 27 turns forward. Consequently, the movable lever 27 separates from the terminal 35 and contacts a terminal 36. At this point, the other end of the lever 27 is grounded 40 through a case 21 of a sensor (a) and the circuit resistance of an oil pressure gauge 34 drops so sharply to swing the pointer 41 of the gauge 34 significantly.