A rollover determination apparatus for vehicles includes a roll-angular-velocity sensor (1) for detecting, as a roll angular velocity, the rotational angular velocity of a vehicle about a longitudinal axis extending lengthwise through the vehicle, an upward-or-downward-acceleration sensor (2) for detecting, as an upward or downward acceleration, an acceleration in an upward or downward direction of the vehicle, an arithmetic processing unit (4a) for carrying out arithmetic processing on both the roll angular velocity detected by the roll-angular-velocity sensor (1) and the upward or downward acceleration detected by the upward-or-downward-acceleration sensor (2), and a rollover occurrence determining unit (4b) for determining whether the vehicle will roll over based on a processing result of the arithmetic processing unit (4a).