  We analyze the statistics of daily price change of stock market in the
framework of a statistical physics model for the collective fluctuation of
stock portfolio. In this model the time series of price changes are coded into
the sequences of up and down spins, and the Hamiltonian of the system is
expressed by spin-spin interactions as in spin glass models of disordered
magnetic systems. Through the analysis of Dow-Jones industrial portfolio
consisting of 30 stock issues by this model, we find a non-equilibrium
fluctuation mode on the point slightly below the boundary between ordered and
disordered phases. The remaining 29 modes are still in disordered phase and
well described by Gibbs distribution. The variance of the fluctuation is
outlined by the theoretical curve and peculiarly large in the non-equilibrium
mode compared with those in the other modes remaining in ordinary phase.
