  We consider the possibility of using one of the $D$-flat directions in the
minimal supersymmetric standard model (MSSM) as the inflaton. We show that the
flat direction consisting of (first generation) left- and right-handed
up-squarks as well as the up-type Higgs boson may play the role of the inflaton
if dominant part of the up-quark mass is radiatively generated from
supersymmetric loop diagrams. We also point out that, if the R-parity violating
Yukawa coupling is of $O(10^{-7})$, $R$-odd $D$-flat directions may be another
possible candidate of the inflaton. Such inflation models using $D$-flat
directions in the MSSM are not only testable with collider experiments but also
advantageous to resolve the problem how the inflaton reheats the universe.
