An object of the present invention is to provide a novel compound that is an agonist of guanosine-3,5-cyclic monophosphate and has an effect of activating protein kinase G. The present invention provides 8-guanosine-3,5-cyclic monophosphate compound which is represented by the following formula, and a pharmaceutical composition, especially a protein kinase G activating agent, which contains the 8-guanosine-3,5-cyclic monophosphate compound as an active ingredient.