A reducing agent injection device , comprising: a honeycomb structure that has a honeycomb structure body with a pillar shape having partition walls defining and forming a plurality of cells which are through channels of a fluid and extend from a first end face being an end face on an inflow side of the fluid to a second end face being an end face on an outflow side of the fluid, and that has a pair of electrode members arranged in a side surface of the honeycomb structure body ; and a urea spraying device that sprays a urea water solution in mist form, wherein each of the pair of electrode members is formed in a band shape extending to a cell extending direction (β) of the honeycomb structure body , and one electrode member of the pair of electrode members is arranged on an opposite side of the other electrode member of the pair of electrode members with respect to a center of the honeycomb structure body sandwiched by the pair of electrode members , in a cross section perpendicular to the cell extending direction (β), and the urea water solution sprayed from the urea spraying device (a2) is supplied inside the cells from the first end face of the honeycomb structure body , and urea in the urea water solution (a1) supplied in the cells is heated and hydrolyzed inside the electrically heated honeycomb structure body to generate ammonia, and the ammonia (b) is discharged outside the honeycomb structure body from the second end face and is injected outside, characterised in that the urea water solution (a1) is sprayed toward the first end face of the honeycomb structure body from the urea spraying device and an angle (θ) between a spraying direction (α) of the urea water solution (a1) from the urea spraying device and a direction parallel to the cell extending direction (β) of the honeycomb structure body and heading to the first end face of the honeycomb structure body from the urea spraying device is from 5° to 60°. a honeycomb structure that has a honeycomb structure body with a pillar shape having partition walls defining and forming a plurality of cells which are through channels of a fluid and extend from a first end face being an end face on an inflow side of the fluid to a second end face being an end face on an outflow side of the fluid, and that has a pair of electrode members arranged in a side surface of the honeycomb structure body ; and a urea spraying device that sprays a urea water solution in mist form, wherein each of the pair of electrode members is formed in a band shape extending to a cell extending direction (β) of the honeycomb structure body , and one electrode member of the pair of electrode members is arranged on an opposite side of the other electrode member of the pair of electrode members with respect to a center of the honeycomb structure body sandwiched by the pair of electrode members , in a cross section perpendicular to the cell extending direction (β), and the urea water solution sprayed from the urea spraying device (a2) is supplied inside the cells from the first end face of the honeycomb structure body , and urea in the urea water solution (a1) supplied in the cells is heated and hydrolyzed inside the electrically heated honeycomb structure body to generate ammonia, and the ammonia (b) is discharged outside the honeycomb structure body from the second end face and is injected outside, characterised in that the urea water solution (a1) is sprayed toward the first end face of the honeycomb structure body from the urea spraying device and an angle (θ) between a spraying direction (α) of the urea water solution (a1) from the urea spraying device and a direction parallel to the cell extending direction (β) of the honeycomb structure body and heading to the first end face of the honeycomb structure body from the urea spraying device is from 5° to 60°. <EOS>