To provide a method for monitoring the opening of a steam control valve, with which an operator can quickly correspond to abnormal conditions in the operation for opening a steam control valve.

This is a method of monitoring the opening of a steam control valve 32 for increasing/decreasing the quantity of steam to be supplied to a turbine 20 for driving a water supply pump 16 in a power generation plant S. An alarm device 70A is operated when a first deviation between the opening of the steam control valve 32 and a target opening thereof becomes a first set value or more.