A nanoscopic understanding of spin-current dynamics is crucial for controlling the spin transport in materials. However, gaining access to spin-current dynamics at an atomic scale is challenging. Therefore, we developed spin-polarized scanning tunneling luminescence spectroscopy (SP STLS) to visualize the spin relaxation strength depending on spin injection positions. Atomically resolved SP STLS mapping of gallium arsenide demonstrated a stronger spin relaxation in gallium atomic rows. Hence, SP STLS paves the way for visualizing spin current with single-atom precision.