A tool storage device is adapted for retaining a hand tool thereon, and includes a seat engaging component and a storage unit. The seat engaging component includes a web wall, and top and bottom walls cooperating with the web wall to define a receiving space. Each of the top and bottom walls has a distal edge. The distal edges cooperatively define an opening in spatial communication with the receiving space. The storage unit includes a slidable seat that has a connecting portion extending into the receiving space through the opening, a positioning plate connected to an outer end of the connecting portion and mounted with a positioning seat, and upper and lower engaging components disposed in the receiving space, each extending from an inner end of the connecting portion and abutting resiliently against the web wall of the seat engaging component.