  A generalized torsion in a group, an non-trivial element such that some
products of its conjugates is the identity. This is an obstruction for a group
being bi-orderable. Though it is known that there is a non bi-orderable group
without generalized torsions, it is conjectured that 3-manifold groups without
generalized torsions are bi-orderable. In this paper, we find generalized
torsions in the fundamental groups of once punctured torus bundles which are
not bi-orderable. Our result contains a generalized torsion in a tunnel number
two hyperbolic once punctured torus bundle.
