NOVELTY - Producing alcohol from lignocellulosic biomass involvespretreating lignocellulosic biomass as a substrate to obtain a pretreated material for saccharification; saccharifying the pretreated material with a saccharogenic enzyme to obtain a saccharified solution; and fermenting the saccharified solution in the same chamber using a fermentative microorganism cell to obtain a fermented solution containing alcohol; determining concentration levels of an organic acid formed in the saccharified solution; and feeding the fermentative microorganism cell in chamber.    USE - For producing alcohol from lignocellulosic biomass (claimed) such as bioethanol.    ADVANTAGE - The method efficiently carry out the fermentation by analyzing the behaviors during SSF of these factors which affect microorganism cells while controlling the inhibitory factors of fermentative microorganism growth; and avoids reduction in fermentation efficiency caused by the stasis or death of the fermentative microorganism cells due to inhibitory substances produced during the saccharification and fermentation and to carry out the fermentation in the environment with little growth inhibition and fermentation inhibition.    DETAILED DESCRIPTION - Producing alcohol from lignocellulosic biomass involvespretreating lignocellulosic biomass as a substrate to obtain a pretreated material for saccharification; saccharifying the pretreated material with a saccharogenic enzyme to obtain a saccharified solution; and fermenting the saccharified solution in the same chamber using a fermentative microorganism cell to obtain a fermented solution containing alcohol; determining concentration levels of an organic acid formed in the saccharified solution by a measuring unit from the initiation to completion of the saccharification; and feeding the fermentative microorganism cell by predetermining an average change rate of the organic acid concentration per unit of time from the organic acid concentration levels determined at respective time points by the measuring unit, and by determining a timing of feeding the fermentative microorganism cell before the average change rate increases in consideration of a time length required for the fermentative microorganism cell to grow.