  There have been theoretical and experimental studies on quantum nonlocality
for continuous variables, based on dichotomic observables. In particular, we
are interested in two cases of dichotomic observables for the light field of
continuous variables: One case is even and odd numbers of photons and the other
case is no photon and presence of photons. We analyze various observables to
give the maximum violation of Bell's inequalities for continuous-variable
states. We discuss an observable which gives the violation of Bell's inequality
for any entangled pure continuous variable state. However, it does not have to
be a maximally entangled state to give the maximal violation of Bell's
inequality. This is attributed to a generic problem of testing the quantum
nonlocality of an infinite-dimensional state using a dichotomic observable.
