We generally tend to discount the satisfaction induced by the consumption in the future relative to the satisfaction at present. We feel more attractive to the immediate reward even if it is not a great amount of money. This is called primacy of immediate reward. Therefore, it is possible that this property forces us to put immediate profits or rewards before those in the future especially when the incentive to immediate awards or profits is stronger. It is speculated that such a property leads to cognitive biases to commit violation, and at the worst case causes a crucial accident such as the critical mass accident at the uranium processing plant of JCO Tokai Works Test Facility. As the basis for the prevention of violation-based human error, the primacy of immediate reward was explored in detail and an attempt was made to identify the condition under which the primacy of immediate reward is dominant. The primacy of immediate reward did not always arise, and it readily occurred under the following situation: (1) very uncertain situation under which a promise is not necessarily observed, and (2) situation under which one feels much starved and need money to eat something with. It was found that the urged to gain an immediate reward readily led to time discount.