The present invention provides a compound that has inhibiting activity against mPGES-1 and is useful in the prevention or treatment of pain, rheumatoid arthritis, osteoarthritis, fever, Alzheimer's disease, multiple sclerosis, arteriosclerosis, glaucoma, ocular hypertension, ischemic retinoapthy, systemic scleroderma and/or malignant tumor such as colon cancer. The present invention relates to the compound of formula [I-a], [I-b], or [I-c] or a pharmaceutically acceptable salt thereof. (Each symbol in the formulas is as defined in the description.)
