With the increase in intensity and energy of high-power lasers, it became possible to generate kiloteslaclass magnetic fields that can be applied to high-energy-density physics experiments. The application of magnetic field broadens the interdisciplinary sciences covered by the high-energy-density-physics. In this article, we will introduce the generation of a strong magnetic field with a capacitor-coil and a sail targets driven by a high-power laser. Kilotesla magnetic field improves the quality of fast electron and ion beams produced by a high-power laser. We describe hydrodynamic instability caused by the anisotropy of thermal conduction in the external magnetic field, and the relativistic magnetic reconnection and particle acceleration associated with reconnection in high energy magnetized plasma, and finally, the challenge to 10 kT will be discussed.