In acoustic emission studies on granite under uniaxial compression, clear hysteresis of emission numbers related to the stress history (Kaiser effect) was observed below dilatancy onset stress. The maximum stress loaded in the past is memorized in rocks. Above dilatancy, we could not observe such a hysteresis. These features are explained by the nature of irreversible sudden advances of microcrack tips. Recovery process time of this hysteresis is over one month under room humidity and temperature conditions. The results in this paper cast foundation for the applicability of geostress measurements by the acoustic emission method.