A device that produces a sugar solution from cellulose-containing biomass includes: a horizontal reaction tank that includes a stirring shaft provided along a horizontal direction in the horizontal reaction tank and a stirring blade provided to the stirring shaft, the horizontal reaction tank being configured to obtain a saccharified slurry by reacting the cellulose-containing biomass with a saccharification enzyme by stirring the cellulose-containing biomass and the saccharification enzyme; a vertical reaction tank configured to obtain a saccharified liquid by saccharifying the saccharified slurry; a saccharified slurry feed line that connects the horizontal reaction tank and the vertical reaction tank; and a warming part provided around the horizontal reaction tank or on a wall surface of the horizontal reaction tank and heats the horizontal reaction tank.