The present invention relates to a pyrimidine compound represented by the following formula [I] wherein each symbol is as defined in the specification, a pharmaceutically acceptable salt thereof, and a pharmaceutical agent for the prophylaxis or treatment of a disease caused by undesirable cell proliferation, particularly an antitumor agent, which contains such compound. The compound of the present invention has superior undesirable cell proliferation suppressing action, particularly, an antitumor action, and is useful as an antitumor agent for the prophylaxis or treatment of cancer, antirheumatoid agent and the like. In addition, by the combined use with other antitumor agent such as alkylating agent, metabolism antagonist and the like, it can be a more effective antitumor agent.
