Abstract: A method for removing a heavy metal from sludge, including the step of putting the sludge into contact with a treating liquid to dissolve the heavy metal contained in the sludge into the treating liquid. The treating liquid is formed of either A or B, where (A) is an aqueous solution of phosphoric acid, and (B) is an aqueous solution of phosphoric acid containing at least one of B1 and B2, where (B1) is at least one acid other than phosphoric acid, and (B2) is at least one oxidant. The concentration of the phosphoric acid in the treating liquid is 3% by weight or more. Alternatively, the sludge is put into contact with the treating liquid at a temperature of 40.degree. C. or higher.