In a nondestructive testing apparatus for testing normality of a blade root in a steam turbine installed in a nuclear plant or a thermal plant, an ultrasonic probe and an encoder can be mounted at the outside by only removing a casing of the steam turbine, without the necessity of withdrawing a turbine rotor, so that an automatic testing can be performed by rotating the steam turbine. Since the testing result can be digitally stored, reliability of the testing is improved. Furthermore, size of the testing apparatus is highly reduced for a tester to conveniently carry and install the testing apparatus alone. As a result, installation time and the whole testing time can be minimized.