1. A method for separating cellulose from a wood-based raw material including hemicellulose, cellulose, and lignin as principal components, the method comprising the steps of:injecting the wood-based raw material into a dissolution reservoir in which ethylene glycol is stored as a separating agent, and heating the separating agent in the dissolution reservoir at atmospheric pressure to a temperature in a range of 260° C. to 280° C., and
reacting the wood-based raw material with the separating agent, evaporating a hemicellulose component from the separating agent and condensing the hemicellulose component, monitoring a pH value of the condensate of the hemicellulose component, wherein the pH value changes from an acidic value to a neutral value as a temperature of the separating agent increases, the temperature of the condensate is held at the temperature at which a change in the pH value of the condensate decreases, lignin is dissolved in the separating agent, and crude cellulose that floats in the separating agent is separated and collected.