A phosphorus-substituted isoprenoid derivative represented by general formula (I) or a pharmacologically acceptable salt thereof, useful for preventing and treating diseases for which a squalene synthetase inhibition is efficacious. In formula (I), R¹ and R² represent each hydrogen, lower alkyl, cycloalkyl, alkenyl, alkynyl, aryl which may be substituted, arylalkyl which may be substituted on the aryl moiety, heteroaryl or heteroarylalkyl; R³ and R⁴ represent each hydrogen, lower alkyl or alkali metal; Y represents -P(O)(OR⁵)(OR⁶) (wherein R⁵ and R⁶ represent each hydrogen, lower alkyl or alkali metal) or -CO₂R⁷ (wherein R⁷ represents hydrogen, lower alkyl or alkali metal); Z represents -(CH₂) m - (wherein m represents an integer of 0 or 1 to 3), -(CH₂) p -CH=CH-(CH₂) q - (wherein m represents 0 or 1 and q represents 1 or 2), or -A-NR⁸-(CH₂) r - (wherein R⁸ represents hydrogen or lower alkyl, A represents C₁ to C₅ alkylene, and r represents an integer of 0 or 1 to 5); and n represents an integer of 0 or 1 to 5.