Ultra-high-speed motors has frequently been considered for many applications because to increase rotational speed of motors is effective in improving output power density and reducing motor size. In this paper, a 4-pole ultra-high-speed motor with concentrated winding structure is discussed in order to achieve even higher output power density. However, applying 4-pole magnetization to conventional ultra-high-speed motors using Nd sintered permanent magnet (PM) and concentrated winding structure will extremely increase total loss, total loss density, and especially rotor loss density. Therefore, from the viewpoint of cooling and continuous operation, it is important to propose a 4-pole ultra-high-speed motor with concentrated winding structure that can achieve even higher power density without increasing the total loss density and the rotor loss density. This paper shows that there are four important key points in the motor design to realize the proposed motor. It is found that the proposed motor can accomplish 1.5 times higher output power density without increasing the total loss density and the rotor loss density than the conventional 2-pole ultra-high-speed motor with Nd sintered PM and concentrated winding structure.