A compound has inhibitory activity on Discoidin Domain Receptor 1. A urea derivative is represented by the formula (I) or a pharmaceutically acceptable salt thereof: wherein, R1 is trifluoromethyl, trifluoromethoxy, or pentafluorosulfanyl; each R2 is independently a hydrogen atom or methyl which is optionally substituted by one hydroxyl or one saturated heterocyclyl having four to six ring-forming atoms; R3 is a hydrogen atom, halogen atom, C1-C3 alkyl, saturated heterocyclyl having four to six ring-forming atoms and optionally having an oxo group, or R5O—; and R4 is phenyl, pyridyl, pyridazinyl, or pyrimidinyl, which phenyl, pyridyl, pyridazinyl, or pyrimidinyl is optionally substituted by one R6.