We present the first application of pulsed high magnetic fields up to 30T for neutron diffraction experiments. As the first study, field variations of a couple of magnetic Bragg reflections have successfully been measured in the frustrated antiferromagnet TbB4. The results show that the conventional models fail, and a model, which is a mixture of the XY- and the Ising-type moments, matches for the half-magnetization state. We deduce an interaction that stabilizes an orthogonal moment arrangement as an origin of the unusual magnetization plateaus. Our results demonstrate the powerfulness of the present pulsed magnetic fields neutron diffraction system.