A BACE1 inhibitor contains, as the active component, a compound of the following formula (I)(wherein, ring A represents an optionally substituted carbon cyclic group or an optionally substituted heterocyclic group etc., E represents a lower alkylene group etc., X represents S, O or NR1, R1represents a hydrogen atom or an optionally substituted lower alkyl group, each of R2a, R2b, R3a, R3b, R4aand R4bindependently represents a hydrogen atom, a halogen atom, a hydroxy group etc., n and m independently represents an integer of 0~3, n+m represents 1~3, R5represents a hydrogen atom, an optionally substituted lower alkyl group etc.) or the pharmaceutically acceptable salt or the solvate thereof.以如下式(I)化合物:(式中環A為可有取代基之碳環基或可有取代基之雜環基,E為低伸烷基等,X為S、O或NR1,R1為氫或低烷基,R2a、R2b、R3a、R3b、R4a及R4b各自獨立為氫、鹵素、羥基等,n及m各自獨立為0~3之整數,n+m為1~3,R5為氫、可有取代基之低烷基等)或其製藥容許鹽或彼等之溶劑合物為有效成分之BACE1抑制劑。
