The present invention provides a method for manufacturing a virus-free protein drug, comprising (a) a filtration step of filtering a virus-containing protein solution through a small-pore size virus removal membrane to obtain a virus-free protein solution, the filtration step (a) comprising (q) a low-pressure filtration step of filtering the solution through the small-pore size virus removal membrane at a filtration pressure of 0.30 kgf/cm 2 or lower to obtain the virus-free protein solution, wherein the solution prior to filtration in the low-pressure filtration step (q) has a pH (X) and a salt ionic strength (Y (mM)) that satisfy the following equations 1 and 5: 0 ‰¤ Y ‰¤ 150X - 590 (Equation 1) and 3.5 ‰¤ X ‰¤ 8.0 (Equation 5) or the following equations 4 and 5: Y = 0 (Equation 4) and 3.5 ‰¤ X ‰¤ 8.0 (Equation 5).
