To provide a cancer pain therapeutic and/or prophylactic agent which can be administered to a patient for a long period of time from the early stage to the final stage of the cancer pain therapy, instead of conventional non-opioid analgesic agents or opioid analgesic agents. The cancer pain therapeutic and/or prophylactic agent containing, as an active ingredient, a 1,5-benzodiazepine derivative represented by formula (1): (wherein R 1 represents a C 1-6 alkyl group, R 2 represents a phenyl group or a cyclohexyl group, and Y represents a single bond or a C 1-4 an alkylene group) or a pharmaceutically acceptable salt thereof.
