A method for producing high purity terephthalic acid wherein a slurry having an acetic acid solvent and, dispersed therein, crude terephthalic acid crystals which has been prepared by subjecting a p-alkyl benzene to a liquid phase oxidation in a solvent of acetic acid is continuously converted to a water slurry by the mother liquid exchange, and then the resultant water slurry is subjected to a hydrogenation treatment, which comprises introducing the above acetic acid slurry to a tower having a center axis having a plurality of agitating blades at the top thereof, to form a region having a high concentration of terephthalic acid crystals in the tower through the sedimentation of the terephthalic acid crystals, supplying the water for substitution to the bottom of the tower in such a manner to form an upward water flow while generating a revolving flow of the high concentration region by the rotation of the agitation blade, to thereby subject said terephthalic acid crystals and said upward water flow to a counter-flow contact, and taking out the acetic acid from a portion being upper than the supply port for the acetic acid slurry while withdrawing the terephthalic acid crystals having contacted with the upward water flow together with the water for substitution from the tower bottom. The above method allows the substitution of the acetic acid solvent of the acetic acid slurry with water, with a high substitution percentage.