A method of disintegrating pulp for use in cellulose acetate production includes: a primary disintegration step of disintegrating a pulp sheet into pulp pieces having an average area of not more than 45 cm 2 ; and a secondary disintegration step of disintegrating the pulp pieces with an impact shock exerted by a jet mill (20). The jet mill (20) includes: a cylindrical casing (21) provided with an inlet (21d) and an outlet (21 e); and a rotor (25) including a plurality of blades (25a) provided on its outer peripheral portion, the plurality of blades (25a) facing an inner peripheral surface of the casing (21).
