A method of producing a platelet solution replaced with an artificial preservation solution includes a filtering step of carrying out cross-flow filtration of a platelet solution under the conditions of Formula (1) at an inlet wall shear rate of 25 to 1500 s−1 using a separation membrane whose surface which contacts with the platelet solution has an average pore size of not less than 0.1 μm and less than 2.0 μm, thereby obtaining a concentrated platelet solution and a mixing step of mixing the concentrated platelet solution with an artificial preservation solution to obtain the platelet solution replaced with an artificial preservation solution:1.0×1011<(A×B)/(γ×μP)≦2.5×1013 (platelets/(hr·m2·Pa)) (1)A: Concentration of platelets contained in the platelet solution (platelets/mL with the proviso that the range is 8.0×107 to 200×107 platelets/mL)B: Filtration flow rate per unit area (mL/hr/m2)γ: Inlet wall shear rate (s−1)μP: Viscosity of the platelet solution (Pa·s).
