A data management method causing a computer to execute processing comprising: creating, when a predetermined data processing program performs data processing, based on an access frequency to a state item in a data store, high-frequency state item list information obtained by listing high-frequency state items of which the access frequency to the state item is high; determining whether or not state information includes a value of a high-frequency state item, determining, when (i) the state information includes the value of the high-frequency state item, (ii) the high-frequency state item list information exists and (iii) the state information is written to the data store, whether or not the state information is included in the high-frequency state item list information and determining, when the high-frequency state item list information does not exist, whether or not the state information is included in a cache memory; updating, with the state information that includes the value of the high-frequency state item, a grouped state item in the cache memory in which the state information of a plurality of the high-frequency state items are recorded in one record of the data store when it is determined that the state information is included in the high-frequency state item list information or the cache memory; deleting a grouped state information that corresponds to the state information from the cache memory and from the data store, and storing the state information in the cache memory as a new individual entry when it is determined that the state information is not included in the high-frequency state item list information and the cache memory; and, writing contents stored in the cache memory to the data store when flushing control is performed, wherein, in the creating, the high-frequency state item list information is created for a kind of an external device that outputs state information that includes a value of the state information and the state item, and the determining is performed with reference to the high-frequency state item list information that corresponds to the kind of the external device, wherein the predetermined data processing program includes a plurality of predetermined data processing programs for respective event messages input from a plurality of external devices of different kinds, and the plurality of predetermined data processing programs processes the respective kinds of messages, and in the determining, when the state information that includes the value of the state item is written to the data store by the predetermined data processing program, whether or not one or a plurality of the state items included in an event message correspond to the high-frequency state item is determined with reference to the high-frequency state item list information of a corresponding kind of the external device. creating, when a predetermined data processing program performs data processing, based on an access frequency to a state item in a data store, high-frequency state item list information obtained by listing high-frequency state items of which the access frequency to the state item is high; determining whether or not state information includes a value of a high-frequency state item, determining, when (i) the state information includes the value of the high-frequency state item, (ii) the high-frequency state item list information exists and (iii) the state information is written to the data store, whether or not the state information is included in the high-frequency state item list information and determining, when the high-frequency state item list information does not exist, whether or not the state information is included in a cache memory; updating, with the state information that includes the value of the high-frequency state item, a grouped state item in the cache memory in which the state information of a plurality of the high-frequency state items are recorded in one record of the data store when it is determined that the state information is included in the high-frequency state item list information or the cache memory; deleting a grouped state information that corresponds to the state information from the cache memory and from the data store, and storing the state information in the cache memory as a new individual entry when it is determined that the state information is not included in the high-frequency state item list information and the cache memory; and, writing contents stored in the cache memory to the data store when flushing control is performed, wherein, in the creating, the high-frequency state item list information is created for a kind of an external device that outputs state information that includes a value of the state information and the state item, and the determining is performed with reference to the high-frequency state item list information that corresponds to the kind of the external device, wherein the predetermined data processing program includes a plurality of predetermined data processing programs for respective event messages input from a plurality of external devices of different kinds, and the plurality of predetermined data processing programs processes the respective kinds of messages, and in the determining, when the state information that includes the value of the state item is written to the data store by the predetermined data processing program, whether or not one or a plurality of the state items included in an event message correspond to the high-frequency state item is determined with reference to the high-frequency state item list information of a corresponding kind of the external device.