To provide a method and a system for the pretreatment of a lignocellulosic biomass material, enabling it to be continuously treated under high pressures.

The system includes a grinding apparatus 5, which is installed on the downstream side of a closed line 4 into which a lignocellulosic biomass material and water are continuously fed under high pressures in order to put the lignocellulosic biomass material to pretreatment in producing ethanol by converting, to a saccharide by enzymatic saccharification, cellulose obtained from the lignocellulosic biomass material followed by fermenting the thus obtained saccharide. This system also includes a pair of grindstones 10 and 11 standing against each other apart from a spacing t, with one 10 of them fixed and the other 11 disposed rotatably and movably in the direction in a spacing t-variable manner, a driving means 12 functioning to rotate the other grindstone 11 and drive it so as to move in the above direction, a pressure sensor 7 for sensing the inside pressure Pr, and a controller 13 functioning to adjust the spacing t correspondingly to the differential pressure P between a sensed pressure Pr and a desired pressure Pe.