Recently, there has been a growing interest in the safety of nuclear power plants after the Fukushima nuclear accident. Most of the nuclear accidents occur in small bore pipe welds. Most of the small bore pipe welds which are dangerous are located in the high radiation exposure area. Therefore, there is a problem that the high radiation exposure of the workers is inevitable at the time of installation and replacement, and the current small bore pipe welds are not monitored. Therefore, in this study, we try to confirm the vibration characteristics according to the depth of cracks in the test piece simulating the small diameter pipe weld. In the experiment, the resonance region of the specimen was changed according to the crack depth. Experimental results show that the resonance region moves uniformly depending on the presence or absence of cracks. However, it was confirmed that it does not vary linearly with the crack depth. In the next study, we try to simulate an actual small diameter welded joint.