Provided is a nucleic acid aptamer exhibiting binding capacity with respect to a microvesicle. Also provided are: a microvesicle detection/isolation method using said aptamer exhibiting binding capacity with respect to the microvesicle; and a drug delivery system. This nucleic acid aptamer includes: 5'-X1-Ms-X2-3' (Ms represents a base sequence which is at least 80% identical to YRCGGNGGWGTWGGGGR (SED IQ NO: 209)), and X1 and X2 bind complementarily to form stems of 0-50 base pairs); or 5'-X3-(N)m-Mk-(N)n-X4-3' (Mk represents a base sequence which is at least 80% identical to either RRRDDRNDRGRKW (SED ID NO: 208) or RVDDGGGHTCTAC (SEQ ID NO: 211), m and n each represent an integer from 0 to 20, and X3 and X4 bind complementarily to form stems of 0-50 base pairs).
