To provide a compound useful as an active ingredient of a pharmacological composition for the treatment of urinary storage symptoms, dysuria, lower urinary tract diseases, and the like. [Solution] The inventors perfected the present invention after discovering that thiazole derivatives substituted at position 2 by pyrazinylcarbonylamino are exceptional muscarinic M 3 receptor positive allosteric modulators and can be expected to serve as agents for the prevention or treatment of urinary bladder and urinary tract diseases involving bladder contraction mediated by muscarinic M 3 receptors. The 2-acylaminothiazole derivatives or salts thereof of the present invention can be expected to serve as agents for the prevention or treatment of urinary bladder and urinary tract diseases involving bladder contraction mediated by muscarinic M 3 receptors, e.g., underactive bladder and the like.