PROBLEM TO BE SOLVED: To provide a functional nucleic acid molecule directly improving the efficiency of protein synthesis.SOLUTION: According to the present invention, there are provided (a) a functional nucleic acid molecule comprising: a target determining sequence containing an antisense sequence against a target sequence in RNA encoding a protein, which is an object of improving the efficiency of protein synthesis; and a regulatory sequence having an activity of improving the efficiency of protein synthesis, and (b) the use of such a functional nucleic acid molecule. In the functional nucleic acid molecule, the regulatory sequence is a sequence derived from SINE-B2.