Reduction of the loss regions existing in the velocity space plays an important role in improvement of the confinement in the tandem mirror. Particle flow into the loss region affects the axial confinement. The ions being trapped in the magnetic mirror field are scattered from the trapped region into the loss region through the loss boundaries. In order to investigate the fine structure appeared in the loss region, the end-loss energy component analyzer (ELECA) devices have been constructed and located on both sides of the tandem mirror. Three kinds of structures in the loss region were observed in the RF-driven tandem mirror plasma.