The objective of the present invention is to improve the efficiency of screening/selection of a membrane protein in molecular evolutionary engineering (for example, an enzyme evolutionary method).The above-described objective is achieved by providing a unilamellar liposome comprising: (a) a DNA comprising a promoter sequence, a translational initiation sequence, and a sequence encoding a membrane protein; (b) an RNA polymerase; (c) a ribonucleotide; and (d) a cell-free protein synthesis system. In one aspect of the present invention, the membrane protein is a transporter, and the unilamellar liposome further comprises (e) a factor that binds to a ligand transported by the membrane protein.