1. An agreement breach prediction system, comprising: a probability distribution calculation unit that, for each of events that occur in a target system of a service level agreement, calculates a probability distribution of a measured value of a service item included in the service level agreement, on the basis of event information relating to the event and of measured value information relating to the measured value; a probability calculation unit that refers to the probability distribution calculated by the probability distribution calculation unit and to an agreement threshold value of the service item, and that calculates, for each of the events, a probability that applies to a service level agreement breach and a probability that does not apply to the service level agreement breach; a probability density calculation unit that refers to the measured value information, and calculates a probability density of the measured value that applies to the service level agreement breach during a period of time from event occurrence until a predefined time has elapsed, and a probability density of the measured value that does not apply to the service level agreement breach during the period of time from the event occurrence until the predefined time has elapsed; and a breach occurrence probability calculation unit that, when the event occurs, calculates a probability that the agreement breach occurs within the predefined time after the occurrence of the event, by using the respective probabilities corresponding to the event and the respective probability densities corresponding to the measured values at a time of occurrence of the event.