Abstract: An in-car storage box which can be reliably fastened on a seat in a vehicle. A container body 1 is formed with a belt groove 9 substantially orthogonal to the front-to-back direction of the container body 1. A seat belt B is hung on the belt groove 9 and tightened, so that the storage box can be firmly fastened onto the seat. Thus, it is possible to prevent the storage box from being moved within the vehicle even though a force of inertia is exerted thereupon by stepping on a brake or the like. Further, as at least one side of the belt groove is formed with a hook, the seat belt can stay in the belt groove without coming off there, thus ensuring the fastening of the seat belt. Still further, as the belt groove 9 is formed on an extension portion 7 which extends toward the inside of an opening 9, it is possible to make the storage box compact as a whole.