PURPOSE: To display the load values of various kinds of hydraulic jack having different pressure receiving areas by multiplying the pressure of the hydraulic jack by a factor corresponding to the pressure receiving area of the jack by a pressure displaying means.

CONSTITUTION: A signal detected by a distortion gauge 1 fitted to the hydraulic jack A is amplified and the pressure and load values are displayed on a digital indicator 9. The indicator 9 is adjusted by span adjusting and zero point correcting variable electric elements 3, 4. The hydraulic jack A, the indicator 9, a pressure sensor B, and a pump F are connected to an Amsler universal tester E to read out the pressure display value of the indicator 9 and a load display value of the Amsler universal tester. Then, a factor regulating variable electric element 7 for multiplying the pressure receiving area of the jack is connected to the indicator 9 through a changeover switch 8 and the factor is adjusted so that digitally displayed value becomes the load display corresponding to the pressure indication.