Structure for arranging additive tank for vehicle

In a structure for arranging an additive tank for a vehicle that includes: a particulate filter for trapping particulate matter in an exhaust gas which is exhausted from a diesel engine; and an additive tank for containing an additive which lowers a combustion temperature of the particulate matter which is trapped by the particulate filter, the additive tank is arranged between a floor panel which is fixed to right and left side members, and a cross member which is provided so as to bridge the right and left side members.