A tool holder holding and loosening device of chain-type tool magazine of a machine tool is disclosed. A locking mechanism is disposed on a rear end of each of sockets in a tool magazine. The locking mechanism is adapted to abut against an end of a tool holder mounted in the socket, thereby to prevent the tool holder from accidentally loosing. A tool loosening device is disposed on a predetermined position of the chain-type tool magazine. The tool loosening device is adapted to unlock the locking mechanism of the tool magazine passing through the predetermined position, so that the tool holder could be easily taken out of the socket.