  We discuss generation of non-Gaussianity in density perturbation through the
super-horizon evolution during inflation by using the so-called $\delta N$
formalism. We first provide a general formula for the non-linearity parameter
generated during inflation. We find that it is proportional to the slow-roll
parameters, multiplied by the model dependent factors that may enhance the
non-gaussianity to the observable ranges. Then we discuss three typical
examples to illustrate how difficult to generate sizable non-Gaussianity
through the super-horizon evolution. First example is the double inflation
model, which shows that temporal violation of slow roll conditions is not
enough for the generation of non-Gaussianity. Second example is the ordinary
hybrid inflation model, which illustrates the importance of taking into account
perturbations on small scales. Finally, we discuss Kadota-Stewart model. This
model gives an example in which we have to choose rather unnatural initial
conditions even if large non-Gaussianity can be generated.
