Intermediates represented by the following general formula (I), etc. which are useful in producing phenoxyacetic acid derivatives represented by the following general formula (X) or pharmaceutically acceptable salts thereof having an effect of stimulating β3-adrenalin receptor and being useful as preventives or remedies for obesity, hyperglycemia, diseases caused by enteric movement disorders, urinary frequency, urinary incontinence, depression or biliary calculus; a process for producing these intermediates; and a method of using the same: (I) (X) wherein R1 and R2 independently represent each lower alkyl.