As robots are no longer just working labors in the industrial fields, but stepping into the human``s daily lives, interaction and communication between human and robot is becoming essential. For this social interaction with humans, a mood-emotion generation model considering believability, diversity, simplicity and deliberation is proposed. First, the OCC model is simplified and then stochastic approach on emotion decision algorithm for believability and diversity is applied. The concept of mood is implemented in order to grant intelligence of considering circumstantial factors. The proposed model is implemented on a 3D robot expression simulator, Doldori, that can express the Ekman``s six basic emotions through its facial expression, gesture, led and so on. Several demonstrations of the model are provided and analyzed as results.