Heterocyclic derivative and pharmaceutical drug

1 2 The present invention provides a novel heterocyclic derivative or a pharmaceutically acceptable salt thereof. For example, the present invention provides a heterocyclic derivative of the general formula [1] or its tautomer, or a pharmaceutically acceptable salt thereof: wherein Rand Rare the same or different aromatic rings, etc., and ring A is a heterocyclic ring. The compound of the invention or a pharmaceutically acceptable salt thereof has potent mPGES-1 inhibiting activity and is useful as an agent for the treatment or prevention of a disease, such as rheumatoid arthritis, osteoarthritis, temporomandibular joint disorders, low back pain, endometriosis, dysmenorrhea, overactive bladder, malignant tumors or neurodegenerative disease.