A method of producing terephthalic acid, comprising steps of: introducing starting terephthalic acid slurry into an upper part of a dispersion medium replacement tower, the starting terephthalic acid slurry containing a dispersion medium and crude terephthalic acid obtained through liquid-phase oxidation of a p-phenylene compound; bringing the starting terephthalic acid slurry into contact with an upward flow of a second dispersion medium introduced from a lower part of the dispersion medium replacement tower to form, in a lower compartment of the dispersion medium replacement tower, a layer of slurry of a purified terephthalic acid crystal dispersed in the second dispersion medium; discharging the slurry of the purified terephthalic acid crystal from the lower compartment of the dispersion medium replacement tower and delivering the slurry to a crystallization chamber provided with a unit for measuring slurry concentration; and delivering the slurry in the crystallization chamber to a solid-liquid separation unit to separate a terephthalic acid crystal, wherein the following conditions to are maintained by regulating a flow rate of the second dispersion medium supplied to the lower compartment of the dispersion medium replacement tower, the flow rate of the slurry of the purified terephthalic acid crystal which is discharged from the lower compartment of the dispersion medium replacement tower, and the flow rate of the slurry delivered from the crystallization chamber to the solid-liquid separation unit: volume V 1 of the slurry in the crystallization chamber is in a range of 0.050 to 0.80 times with respect to volume V 0 of the whole terephthalic acid slurry in the dispersion medium replacement tower; a position of an interfacial region between the layer of the slurry of terephthalic acid crystal which is formed in the lower compartment of the dispersion medium replacement tower and a dilute terephthalic acid slurry in a middle part of the dispersion medium replacement tower is in a variation range of ±800 mm from a control target level; and the slurry concentration in the crystallization chamber is in a range of 25 to 40 mass%. introducing starting terephthalic acid slurry into an upper part of a dispersion medium replacement tower, the starting terephthalic acid slurry containing a dispersion medium and crude terephthalic acid obtained through liquid-phase oxidation of a p-phenylene compound; bringing the starting terephthalic acid slurry into contact with an upward flow of a second dispersion medium introduced from a lower part of the dispersion medium replacement tower to form, in a lower compartment of the dispersion medium replacement tower, a layer of slurry of a purified terephthalic acid crystal dispersed in the second dispersion medium; discharging the slurry of the purified terephthalic acid crystal from the lower compartment of the dispersion medium replacement tower and delivering the slurry to a crystallization chamber provided with a unit for measuring slurry concentration; and delivering the slurry in the crystallization chamber to a solid-liquid separation unit to separate a terephthalic acid crystal, wherein the following conditions to are maintained by regulating a flow rate of the second dispersion medium supplied to the lower compartment of the dispersion medium replacement tower, the flow rate of the slurry of the purified terephthalic acid crystal which is discharged from the lower compartment of the dispersion medium replacement tower, and the flow rate of the slurry delivered from the crystallization chamber to the solid-liquid separation unit: volume V 1 of the slurry in the crystallization chamber is in a range of 0.050 to 0.80 times with respect to volume V 0 of the whole terephthalic acid slurry in the dispersion medium replacement tower; a position of an interfacial region between the layer of the slurry of terephthalic acid crystal which is formed in the lower compartment of the dispersion medium replacement tower and a dilute terephthalic acid slurry in a middle part of the dispersion medium replacement tower is in a variation range of ±800 mm from a control target level; and the slurry concentration in the crystallization chamber is in a range of 25 to 40 mass%. volume V 1 of the slurry in the crystallization chamber is in a range of 0.050 to 0.80 times with respect to volume V 0 of the whole terephthalic acid slurry in the dispersion medium replacement tower; a position of an interfacial region between the layer of the slurry of terephthalic acid crystal which is formed in the lower compartment of the dispersion medium replacement tower and a dilute terephthalic acid slurry in a middle part of the dispersion medium replacement tower is in a variation range of ±800 mm from a control target level; and the slurry concentration in the crystallization chamber is in a range of 25 to 40 mass%.