The present disclosure provides an apparatus for manufacturing a silicon substrate for solar cells using continuous casting, which can improve quality, productivity and energy conversion efficiency of the silicon substrate. The apparatus includes a crucible unit configured to receive raw silicon and having a discharge port, a heating unit provided to an outer wall and an external bottom surface of the crucible unit and heating the crucible unit to form molten silicon, a casting unit casting the molten silicon into a silicon substrate, a cooling unit rapidly cooling the silicon substrate, and a transfer unit disposed at one end of the cooling unit and transferring the silicon substrate. The casting unit includes a casting unit body having a casting space defined therein to be horizontally connected to the discharge port, and an assistant heating mechanism that preheats the casting unit body to control a solidification temperature of the silicon substrate.