1. A power system data model conversion method, comprising: an instance readout step of reading out all instances from a database which stores devices of a power system in an object format according to an object-oriented data model; a connected relation analysis step of following a connected relation of a main device, which is among the devices and subject to power system analysis, with the other devices which are connected to the main device; and a property information aggregation step of aggregating property information recorded in one or more of the instances into a single instance and also erasing the instance unnecessary for the power system analysis on the basis of the analysis result in the connected relation analysis step to create a power system analysis data model.