Disclosed are benzothiazine derivatives represented by the following formula (I): wherein the dashed line indicates the presence or absence of a bond; Z represents one of the following groups: in which R1 and R2 individually represent alkyl, aralkyl or the like, R3 represents H, alkyl or the like, R4 represents H, aralkyl or the like, X1, X2 and X3 individually represent O or S, and G represents substituted or unsubstituted ethylene, trimethylene or the like.