The present invention pertains to the improvement of a miRNA inhibitor (a synthesized Tough Decoy (S-TuD)). The present invention provides a miRNA inhibitory complex including RNA or an analog thereof, wherein the RNA inhibitory complex includes at least one double-stranded structure and a miRNA binding sequence, each of two strands of the miRNA binding sequence being bound to two strands of at least one end of the double-stranded structure, and the miRNA inhibitory complex further includes at least one crosslinked nucleic acid.