The present invention provides a cell-free protein synthesis method characterized by a cell-free protein synthesis reaction solution that is weakly reducing and suitable for protein folding, performing a weakly reducing synthesis reaction, and preferably performing a translation reaction with the further addition of a substance catalyzing a disulfide bond exchange reaction at the beginning of the translation reaction. This method allows for proper formation of intramolecular disulfide bonds in the protein and efficiently provides protein having substantially the same function as the original protein. Specifically, it provides antibody protein that binds specifically to an antigen.