PURPOSE: To provide the pressure reducing valve which has a protecting function for relieving secondary pressure if the pressure rises abnormally.

CONSTITUTION: The opening extent of a valve hole 9 which links a primary side 7 and a secondary side 8 is controlled by a valve body 12 which is connected to a valve shaft 11 and a thrust in a valve opening direction which is applied by a main spring 18 and a thrust in a valve closing direction which is generated by a main diaphragm 17 by receiving secondary-side pressure are transmitted to the valve shaft 11 to control the opening extent of the valve hole 9 by the difference between those thrusts. This pressure reducing valve A is provided with a relief valve 50 which discharges secondary-side liquid to the outside when the secondary pressure reaches a certain value or above. Consequently, when the secondary pressure exceeds the certain value, the relief valve operates to discharge the secondary-side liquid to the outside, so a member which is applied with the secondary side pressure can be prevented from being damaged.