An objective of the present invention is to improve the solubility of 3-[2-fluoro-5-(2,3-difluoro-6-methoxybenzyloxy)-4-methoxyphenyl]-2,4-dioxo-1,2,3,4-tetrahydrothieno[3,4-d]pyrimidine-5-carboxylic acid. The present invention provides 3-[2-fluoro-5-(2,3-difluoro-6-methoxybenzyl-oxy)-4-methoxyphenyl]-2,4-dioxo-1,2,3,4-tetrahydrothieno[3,4-d]pyrimidine-5-carboxy lic acid choline salt has excellent solubility and storage stability.
