To provide a technology for introducing a PMO with remarkably enhanced cell permeability, leading to significantly enhanced introduction efficiency to thereby provide a therapeutic drug that dramatically ameliorates a medical condition of DMD. Also provided is a therapeutic drug for Duchenne muscular dystrophy, including as an active ingredient a Bubble liposome having a specific morpholino oligomer (PMO) bound to a surface thereof, in which the PMO is introduced into a muscle fiber (muscle cell) of a muscle tissue with high efficiency by administration of the therapeutic drug into the muscle tissue or into a blood vessel followed by ultrasound irradiation to the muscle tissue transcutaneously.