A collision determining apparatus for a vehicle includes a first acceleration measuring device which measures an acceleration acting on the vehicle, a movement amount calculating device which calculates an amount of movement of an occupant, a change in movement speed calculating device which calculates a change in movement speed of the occupant, a first collision determining threshold value setting device which sets collision determining threshold values for a correlation between the amount of movement of the occupant and the change in movement speed of the occupant, a first collision determining device which determines whether or not the correlation exceeds the collision determining threshold value, and a first control signal generating device which generates a control signal which instructs that an occupant protection apparatus be operated slowly in multiple stages or be operated rapidly in multiple stages.