An oil pressure switch, which is connected in an oil path of a piston oil cooling jet to diagnose oil pressure, includes an upper body and a lower body, in which a plunger vertically moves according to oil pressure; a fixing plate that is disposed between the upper body and the lower body; a moving plate that selectively contacts a fixing plate according to movement of the plunger; a spring that generates an elastic force in a direction in which the moving plate selectively contacts the fixing plate; an output terminal that outputs an output signal according to contact between the moving plate and the fixing plate; and a parallel resistor that is electrically connected with the output terminal and electrically connected with a control resistor of a controller.