To provide an assembling method for an exhaust emission control device capable of satisfying both inserting function and holding function without degradation of exhaust emission, curl up of a sheet, or winding of the sheet.

(1) This assembling method of the exhaust emission control device 10 holds a porous carrier 1 from a casing 3 via a mat 2 of ceramic fiber. The assembling method comprises a process of winding the mat 2 on the porous carrier 1, a process of infiltrating liquid into the mat 2 and compressing it or compressing the mat and infiltrating the liquid into it, a process of freezing the compressed mat 2 containing the liquid, and a process of inserting the porous carrier 1 wound with the mat 2 into the casing 3 while the mat 2 is frozen. (2) The assembling method has a process of releasing the freezing of the mat 2 or naturally releasing the freezing after the process of inserting the porous carrier 1 wound with the mat 2 into the casing 3.