Disclosed is a transformed cell (a cell model) which can form a cytoplasmic inclusion body derived from TAR DNA-binding protein of 43 kDa (TDP-43) that is found in the brain of a patient suffering from a neurodegenerative disease such as FTLD and ALS. The transformed cell is characterized by having, introduced therein, a promoter capable of functioning in a host cell and a mutant TDP-43 gene.