The present invention provides a fabrication abnormality detection system for a three-dimensional additive manufacturing device that irradiates a powder bed with beams for additive manufacturing. Thefabrication abnormality detection system determines that the powder bed is abnormally laid when at least one of a first condition and a second condition is satisfied on the basis of results of measurement of the surface shape of the powder bed, the first condition being such that the average height of the powder bed with respect to a reference position of the powder bed deviates from a first defined range and the second condition being such that a variation in height of the powder bed deviates from a second defined range.