[Problem] A compound which is useful as an active ingredient of a pharmaceutical composition for treating storage dysfunctions, voiding dysfunctions, and lower urinary tract diseases is provided. [Means for Solution] The present inventors have found that a thiazole derivative having pyrazine-2-carbonylamino substituted at the 2-position is an excellent muscarinic M 3 receptor positive allosteric modulator, and is useful as an agent for preventing and/or treating bladder or urinary tract diseases, related to bladder contraction by a muscarinic M 3 receptor, thereby completing the present invention. The 2-acylaminothiazole derivative or a salt thereof of the present invention can be used as an agent for preventing and/or treating bladder or urinary tract diseases, related to bladder contraction by a muscarinic M 3 receptor, for example, voiding dysfunctions such as underactive bladder.
