1. A business flow distributed processing system, comprising: a plurality of process servers, each having a generator that generates a process instance that a series of transaction events are arranged in a time sequence; and a master server that reads out event data regarding a transaction event and including an event name, a processing time and an identifier to identify the process instance, from an event data storage unit, and allocates the event data to any one of the plurality of process servers, and wherein the master server comprises: a unit to output an inquiry of a holding state of a process instance corresponding to an identifier included in the event data read out from the event data storage unit to the plurality of process servers; a unit to receive a response for the inquiry from the plurality of process servers and judge whether a plurality of first process servers holding the process instance relating to the inquiry exist; a unit to determine a second process server that is a merge destination of the process instance relating to the inquiry, from among the plurality of first process servers when the plurality of first process servers exist; and a unit to output a merge instruction including information of the second process server and the identifier of the process instance relating to the inquiry to the first process servers, and wherein each of the plurality of process servers comprises: a process instance data storage unit storing the process instance including the event data in association with the identifier of the process instance; a unit, in response to the inquiry from the master server, to search the process instance data storage unit for the identifier relating to the inquiry, and to reply with presence or absence of the process instance relating to the inquiry to the master server; a unit to output event data relating to the identifier included in the merge instruction to the second process server relating to the merge instruction, when the merge instruction from the master server is received and the process server itself is one of the first process servers other than the second process server; and a merge unit, in response to receipt of event data from another process server, to merge the received event data to the process instance, which corresponds to the same identifier as the received event data and is stored in the process instance data storage unit.