A door lock apparatus for use in a tape recorder wherein the door can be opened only via tape cassette insertion. The door lock apparatus is located in the lower portion of the cassette insertion hole, and includes a tape cassette guide, installed at a lower end of the insertion hole, which guides the tape cassette by slidingly contacting against the lower surface thereof, and a door locking mechanism installed on the tape cassette guide, to block or release the rotation of the door when rotated, thereby preventing foreign matter from inadvertently being placed inside the tape recorder.