28 to prepare for calculation of the next event data from the tw section 11 thereby finishing the processing of the current event if the current event is determined to be valid in the above determination the processing is continuously performed as follows that is the current event of the ibus register 61 and the event flag data are written in the stm 28 and the contents of the current event are stored in the rsm 26 via a data selector 64 at this time an address in which the current event is to be written is sequentially incremented from for example 34 0000 34 to 34 ffff 34 by an rsm write address counter 65 note that the result of simulation is temporarily written in the twm 23 or etm 24 and read out from the memory after a delay time the simulation result is not written in the rsm 26 as a past event until the event flag data is checked the acc section 12 starts an operation of obtaining an output change next stage event of a next stage cell generated by the current event first the nnm 25a in the nim 25 is accessed by the name address of a net which is latched by the ibus register 61 and in which an event is generated and the name address of a net in which the next stage event may be generated the type of cell and fan out are stored in an.