The present invention provides pyrazole derivatives useful as production intermediates for isoxazoline derivatives having an excellent herbicidal effect and selectivity between crops and weeds as well as processes for producing the same. The pyrazole derivatives or pharmaceutically acceptable salts thereof which are inventive compounds are represented by the general formula [I] or a salt thereof: wherein R1 represents a C1 to C6 alkyl group, R2 represents a C1 to C3 haloalkyl group, R3 represents a hydrogen atom, a C1 to C3 alkyl group which may be substituted with one or more substituents selected from the following substituent group α, or a formyl group, R4 represents a hydrogen atom or a C1 to C3 haloalkyl group, provided that R4 represents a C1 to C3 haloalkyl group in the case that R3 is a hydrogen or a formyl group, and R4 is a hydrogen group or a C1 to C3 haloalkyl group in the case that R3 is a C1 to C3 alkyl group which may be substituted with one or more substituents selected from the following substituent group α.