In order to obtain the design concept on crack arrestor against shear crack propagation, which is known to propagate with velocity of 200 m/s or so in highly pressurized gas pipelines, the phenomenon of fracture arrest was studied experimentally and analytically using the spring-loaded DCB testing. The simulated mechanical crack arrestor was of heavy thickness type, which was introduced to the dull grooved DCB specimen. With this type of specimen of different size arrestors on several steels, the behavior of shear crack propagation and/or arrest around the arrestor was examined by measuring dynamically a crack tip position, load depression and ductile crack opening displacement. The results of experiments were analyzed succesfully by simulated calculation of crack advancing based on the Dugdale model. Further, using the fracture propagating resistance value obtained from the spring-loaded DCB testing without arrestor, the change of ductile crack opening displacement when the crack approaches to an arrestor was also calculated for the prediction analysis purpose and compared with the experimental data obtained. The main results obtained are as follows. (1) The change of ductile crack opening displacement near arrestor, calculated from approximated method with fracture propagating resistance value, coincides well the experimental data and enables us to evaluate quantitatively the effects of arrestor. (2) The increase of arrestor thickness is more effective to the fracture arrest than the increase of arrestor length. (3) It was found also that fracture was arrested when ductile crack opening displacement at the arrestor front decreased to the level less than that at unstable onset of shear fracture propagation.