A three-dimensional shaping method utilizing a powder layer forming step, and a sintering step with a laser beam or electron beam, the method including the steps of a) measuring the reflection intensity of the beam irradiated in each sintering step, or the reflection intensity of other light, b) commanding to continue sintering within the next time unit, or when the next powder layer forming step is given, when it has been detected that the reflection intensity of the step a) is within a standard range for a given time unit, and, c) judging that a sintering defect has been produced, and commanding to cancel sintering in the next time unit, or when the next powder layer forming step is given, when it is detected that a condition has occurred in which the reflection intensity of step a) deviates from the standard range for a given time unit.