HIS (hospital information system) and PACS (picture archiving and communication system) have become widely popular in clinical offices, and use of RIS (radiology information system) in the department of radiology has spread, creating networking between HIS, PACS, and diagnostic systems. RIS receives patient data and order data from HIS and sends them to the diagnostic systems. On the other hand, the RIS sends the implementation record and accounting data to HIS. When receiving and transmitting of these data are done by the RIS, the event's time is recorded in the RIS as attendant data. This paper proposes a way to analyze patient flow from the records of the event's time. The method counts the number of the accepted examinations y(i) (i = 0, 1, ... N) and the completed examinations z(i) every divided time t from the RIS work list, and computes the following three characteristic values related to patient flow. Those values are average expended time T; T = ( Sigma z(i ) i t - Sigma y(i ) i t ) / Sigma y(i) ,number of exam queue q(i); q(i) = Sigma y(i) - Sigma z(i) , and dissolved time of queue w(i); w(i) = q(i ) ( t / z(i) ). The method analyzes patient flow of radiology using these characteristic values. It also performs a simulation of the flow in cases of equipment trouble.