  We present the galaxy luminosity functions (LFs) of four Hickson Compact
Groups using image data from the Subaru Hyper Suprime-Cam. A distinct dip
appeared in the faint-ends of all the LFs at $M_g\sim-12$. A similar dip was
observed in the LFs of the galaxy clusters Coma and Centaurus. However, LFs in
the Virgo, Hydra, and the field had flatter slopes and no dips. As the relative
velocities among galaxies are lower in compact groups than in clusters, the
effect of galaxy-galaxy interactions would be more significant in compact
groups. The $M_g\sim-12$ dip of compact groups may imply that frequent
galaxy-galaxy interactions would affect the evolution of galaxies, and the dip
in LF could become a boundary between different galaxy populations.
