PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine and a method of detecting deposition of urea, capable of detecting deposition of urea-derived deposits early and precisely.SOLUTION: An exhaust emission control device 2 includes: a first temperature sensor 36 disposed at a lower end of a communication passage 32 downstream of a supply position of urea water and upstream of an SCR catalyst 8; a second temperature sensor 38 disposed at an upper end of the communication passage 32 immediately above the first temperature sensor 36; and a deposition determining part 40 determining whether an absolute value of a difference ΔT between a first temperature Tmeasured by the first temperature sensor 36 and a second temperature Tmeasured by the second temperature sensor 38 is equal to or more than a predetermined threshold. The deposition determining part 40 determines that urea-derived deposits 30 are deposited in the communication passage 32 when the absolute value of the difference ΔT is equal to or more than the predetermined threshold.