PROBLEM TO BE SOLVED: To attain accurate detection of the pressure of a fluid at a high pressure area by detecting the position of a piston moving under the pressure of the fluid with a magnetic linear scale for outputting as linear analog data. SOLUTION: As a piston within a cylinder rises by receiving the pressure of a fluid, a permanent magnet 9 moves along a magnetic linear scale 31 so that a midpoint voltage 22 decreases in proportion to a drop in the internal resistance of a magnetoresistance element R1 and when the midpoint voltage 22 is between reference voltages E1 and E2 (E1 >E2 ) set, outputs of comparators 32 and 33 both go up to a high level to make a voltage work on the base of a transistor 37, turning ON a LED 39. As a result, the output S is turned ON and it is found that the pressure of the fluid reaches a set value. With the pressure switch thus obtained, a detection value of the pressure of the fluid can be adjusted easily by changing a biasing force to the piston facilitating adaptation to a higher pressure of the fluid. This also makes detection possible in a narrow moving area by changing the reference voltages E1 and E2 with a variable resistor 36 to adjust the detection width.