A collision determination ECU includes: a possibility determination section for determining whether or not there is a possibility of a collision with a forward vehicle; a traveling direction determination section for determining whether or not changing of a traveling direction of at least one of an own-vehicle and the forward vehicle is in progress; and a condition changing section for changing a collision determination condition, which is a condition for a possibility estimation section to determine that there is a possibility of a collision, so as to be strict, when the traveling direction determination section determines that changing of a traveling direction is in progress. As a result, unnecessary operations of a passenger protection device and the like can be suppressed.