Disclosed is a radioactive bone diagnostic agent which gives a high ratio of radioactivity accumulation in bone to that in blood from an early stage after administration of the agent and allows capturing an image in a short time after administration. Also disclosed is a bisphosphonic acid derivative represented by the following chemical formula (II) or a salt thereof, wherein X represents —(CH2)mCO—, Y represents —(CH2)n—, R represents H, OH, or a halogen atom, m and n are independent of each other and m represents an integer of 1 to 3, and n represents an integer of 0 to 4.
