Abstract: The present invention relates to tricyclic compounds each represented by the following formula (I): (wherein, R1, R2, R2?, R3, R4, X, Y and Z have the same meanings as defined in the specification); and a drug containing the compound. Since the compounds according to the present invention exhibit an excellent squalene synthetase inhibitory effect and cholesterol synthesis inhibitory effect so that they are useful as a drug such as preventive and/or remedy for diseases in mammals including humans such as hyperlipemia, e.g., hypercholesterolemia, hypertriglyceridemia, and low HDL cholesterolemia and/or arteriosclerosis.