To provide an anti-cancer agent composition, which is excellent in solubility, and has high anti-cancer activity while exhibiting low toxicity.

The anti-cancer agent composition contains a cyclodextrin compound and a phosphine transition metal complex represented by general formula (1). (In the formula, R¹ and R² represent a linear or branched-chain alkyl group, a cycloalkyl group, a cycloalkyl group having a substituent, an adamantyl group, a phenyl group, or a phenyl group having a substituent, have a carbon number between 1 and 10, and may represent the same group or different groups. R3 and R4 represent a hydrogen atom or a linear or branched-chain alkyl group, have a carbon number between 1 and 6, and may represent the same group or different groups. R³ and R⁴ may form a saturated or unsaturated ring by bonding to one another and the saturated or unsaturated ring may have a substituent. M represents a transition metal atom selected from among gold, copper and silver. X^- represents an anion).