The present invention provides drug carriers having high heating efficiency by high-frequency dielectric heating in a state of being selectively accumulated in a target site. The drug carriers each consist of a drug, magnetic fine particles, and a shell containing the drug and the magnetic fine particles. The shell has an outer diameter in a range from 10 nm to 200 nm. The magnetic fine particles having an average particle diameter of d has a standard deviation .sigma. of particle diameter distribution satisfying 0.8d>.sigma.>0.4d. The magnetic fine particles contained in the individual drug carriers generate hysteresis heat due to high-frequency dielectric heating by irradiation of a high-frequency magnetic field.