Novel compounds represented by formula (I) are useful for preventing or treating diseases caused by protozoans. Use is made of one or more members selected from among compounds represented by formula (I), optical isomers thereof and pharmaceutically acceptable salts of the same. In formula (I): X represents a hydrogen atom or a halogen atom R1 represents a hydrogen atom R2 represents a hydrogen atom or a C1-7 alkyl group R3 represents -CHO, -C(=O)R5, -COOR5 [wherein R5 represents a C1-7 alkyl group], -CH2OH or -COOH and R4 represents a C1-16 alkyl group having various substituent(s) on a terminal carbon atom and/or a non-terminal carbon atom, a C2-16 alkenyl group having various substituent(s) on a terminal carbon atom and/or a non-terminal carbon atom, or a C2-16 alkynyl group having various substituent(s) on a terminal carbon atom and/or a non-terminal carbon atom.
