  We show that the diversity in the density slope of the dense wind due to
non-steady mass loss can be one way to explain the spectral diversity of Type
II luminous supernovae (LSNe). The interaction of SN ejecta and wind
surrounding it is considered to be a power source to illuminate LSNe because
many LSNe show the wind signature in their spectra (Type IIn LSNe). However,
there also exist LSNe without the spectral features caused by the wind (Type
IIL LSNe). We show that, even if LSNe are illuminated by the interaction, it is
possible that they do not show the narrow spectra from the wind if we take into
account of non-steady mass loss of their progenitors. When the shock breakout
takes place in the dense wind with the density structure \rho\propto r^{-w},
the ratio of the diffusion timescale in the optically thick region of the wind
(td) and the shock propagation timescale of the entire wind after the shock
breakout (ts) strongly depends on w. For the case w<~1, both timescales are
comparable (td/ts \simeq 1) and td/ts gets smaller as w gets larger. For the
case td/ts\simeq 1, the shock goes through the entire wind just after the light
curve (LC) peak and narrow spectral lines from the wind cannot be observed
after the LC peak (Type IIL LSNe). If td/ts is much smaller, the shock wave
continues to propagate in the wind after the LC peak and unshocked wind remains
(Type IIn LSNe). This difference can be obtained only through a careful
treatment of the shock breakout condition in a dense wind. The lack of narrow
Lorentzian line profiles in Type IIL LSNe before the LC peak can also be
explained by the difference in the density slope. Furthermore, we apply our
model to Type IIn LSN 2006gy and Type IIL LSN 2008es and find that our model is
consistent with the observations.
