The present invention provides a compound useful as an agent for the prophylaxis or treatment of neurodegenerative disease and the like, or a salt thereof.The present invention relates to a compound represented by the formula wherein each symbol is as defined in the specification, or a salt thereof.本發明係提供一種有用於作為預防或治療神經退化疾病等之試劑的化合物或其鹽。本發明係有關一種式(I)所示之化合物或其鹽:其中,各符號係如本說明書所定義。