  A rigorous theory of quantum state reduction, the state change of the
measured system caused by a measurement conditional upon the outcome of
measurement, is developed fully within quantum mechanics without leading to the
vicious circle relative to the von Neumann chain. For the basis of the theory,
the local measurement theorem provides the joint probability distribution for
the outcomes of local successive measurements on a noninteracting entangled
system without assuming the projection postulate, and the quantum Bayes
principle enables us to determine operationally the quantum state from a given
information on the outcome of measurement.
