1. A non-transitory continuous system simulation program product that simulates the behavior of a continuous system constituting a hybrid system together with a discrete system while communicating with a discrete system simulation program that simulates the behavior of the discrete system, the continuous system simulation program product causing a computer to execute the steps of: receiving a request for evaluation of an event generating conditional expression, for an event to be processed by the discrete system simulation program, from the discrete system simulation program, wherein the event generating conditional expression is evaluated by referring to a value of at least one continuous system variable among multiple continuous system variables describing the continuous system; repeating simulation of advancing the current time of the continuous system by a step time interval and evaluation of the event generating conditional expression Until evaluation of the event generating conditional expression indicates true, in response to the receiving of the request for evaluation; recording the value of at least one continuous system variable referred to in simulation of the discrete system before sending the value to the discrete system simulation program; sending current time data indicating the current time and the value of at least one continuous system variable referred to in simulation of the discrete system among the multiple continuous system variables to the discrete system simulation program, in response to evaluation of the event generating conditional expression indicating true; and in the case of sending the value of at least one continuous system variable to the discrete system simulation program in response to evaluation of the event generating conditional expression indicating true, canceling transmission of the value of at least one continuous system variable on condition that the value has not changed.