Single quantum dots (QDs) have been fabricated in an individual single-wall carbon nanotube (SWCNT) simply by depositing source-drain metal on it. The SWCNT between the contacts behaved as a single QD. The single electron transport measurements have been carried out in a dilution refrigerator, which revealed unique artificial atom behavior. Those include clear observation of quantized energy states and their Zeeman splitting in magnetic fields, two or four electron shell structures, and quantum states of an interacting two-electron system. The above characteristics are well modeled by electrons confined in a one-dimensional hard wall potential. The unique features in the SWCNT artificial atom, as compared with semiconductor artificial atoms, are, first, that the single electron charging energy and the quantized level spacing are larger by more than an order, and, second that the simple shell structures are observable even with many electrons in the dot. To demonstrate the larger energy scales for the artificial atom, the teraherz (THz) photon assisted tunneling is presented.