  Detailed neutron diffraction measurements on a single crystalline
ErB$_2$C$_2$ were performed. We observed magnetic diffuse scattering which
consists of three components just above the transition temperatures, which is
also observed in characteristic antiferroquadrupolar ordering compounds
HoB$_2$C$_2$ and TbB$_2$C$_2$. The result of this experiments indicates that
the antiferroquadrupolar interaction is not dominantly important as a origin of
the magnetic diffuse scattering.
