In order to solve various problemes in relation to hammer forging equipment, it is essential to clarify impact stress in hammer forging. However, due to difficulty of making this sort of experiments, there have been few reports of experiments which give us practical figures. Making experiments with model hammers and steam hammers for actual use, the writer has measured by means of Braun tube oscillograph various values of impact force and various relative conditions which are necessary for theoretical design of mount and foundation of forging hammers. From the result of these measurements, practical conditions and figures have been obtained. The writer has also found that shape of the stress greatly varies with material of the article hammered, and that close attention must be paid to the method of measurement for experiments of this kind.