Directional irregular waves have been widely generated in a wave basin with side-wall reflections, and utilized for sea keeping and ocean engineering tests. It is, however, well known that line spectra are generated in a basin with perfect side-wall reflections and that the directions of the line spectra are determined only by the tank width and the wave frequency. This paper shows comparisons of the solutions of the linear theory and designed spectra as well as analyzed results by MLM method of measured data in Yokohama National University. Effects of the number of unit wave makers, the width of the basin and the wave frequency on the generated directional spectra are discussed.