A pseudo-Ising model quantum computation device comprising: a degenerate optical parametric oscillator which causes degenerate optical parametric oscillation of a plurality of pseudo spin pulses corresponding to a plurality of spins in the Ising model and having an identical oscillation frequency; a ring resonator which circularly propagates the plurality of pseudo spin pulses; a temporary spin measuring unit which temporarily measures pseudo spins of the plurality of pseudo spin pulses by temporarily measuring phases of the plurality of pseudo spin pulses every time the plurality of pseudo spin pulses circularly propagate in the ring resonator, and suspends measurement after one set of measurements is completed before another set of measurements is restarted; an interaction computing unit which temporarily computes all interactions relating to the plurality of pseudo spin pulses, on the basis of the coupling coefficients of the Ising model and the pseudo spins of the plurality of pseudo spin pulses which the temporary spin measuring unit has most recently measured, after the temporary spin measuring unit completes one set of measurements before the temporary spin measuring unit restarts another set of measurements; an interaction implementing unit which temporarily implements magnitudes and signs of all the interactions relating to the plurality of pseudo spin pulses which the interaction computing unit has most recently computed, by controlling amplitudes and phases of light injected to the plurality of pseudo spin pulses, after the interaction computing unit completes a temporary computation of all the interactions relating to the plurality of pseudo spin pulses; and a pseudo spin measuring unit which measures the pseudo spins of the plurality of pseudo spin pulses by measuring the phases of the plurality of pseudo spin pulses after the plurality of pseudo spin pulses reach a steady state while a feedback loop constituted by steps performed by the temporary spin measuring unit, the interaction computing unit, and the interaction implementing unit is repeated. a degenerate optical parametric oscillator which causes degenerate optical parametric oscillation of a plurality of pseudo spin pulses corresponding to a plurality of spins in the Ising model and having an identical oscillation frequency; a ring resonator which circularly propagates the plurality of pseudo spin pulses; a temporary spin measuring unit which temporarily measures pseudo spins of the plurality of pseudo spin pulses by temporarily measuring phases of the plurality of pseudo spin pulses every time the plurality of pseudo spin pulses circularly propagate in the ring resonator, and suspends measurement after one set of measurements is completed before another set of measurements is restarted; an interaction computing unit which temporarily computes all interactions relating to the plurality of pseudo spin pulses, on the basis of the coupling coefficients of the Ising model and the pseudo spins of the plurality of pseudo spin pulses which the temporary spin measuring unit has most recently measured, after the temporary spin measuring unit completes one set of measurements before the temporary spin measuring unit restarts another set of measurements; an interaction implementing unit which temporarily implements magnitudes and signs of all the interactions relating to the plurality of pseudo spin pulses which the interaction computing unit has most recently computed, by controlling amplitudes and phases of light injected to the plurality of pseudo spin pulses, after the interaction computing unit completes a temporary computation of all the interactions relating to the plurality of pseudo spin pulses; and a pseudo spin measuring unit which measures the pseudo spins of the plurality of pseudo spin pulses by measuring the phases of the plurality of pseudo spin pulses after the plurality of pseudo spin pulses reach a steady state while a feedback loop constituted by steps performed by the temporary spin measuring unit, the interaction computing unit, and the interaction implementing unit is repeated.