A side airbag apparatus for a vehicle has a gas generator with gas ports, an airbag. With gas injected from the gas ports, the airbag is deployed and inflated between a side portion of a body of the vehicle and a passenger seated on a seat provided in a passenger compartment. The airbag has first and second inflation portion. The first inflation portion is deployed and inflated at a position that corresponds to a shoulder of a passenger having a small physical size. The second inflation portion communicates with the first inflation portion. The second inflation portion is deployed and inflated at a position that corresponds to the abdomen of the passenger having a small physical size. The gas ports are arranged such that gas injected from the gas ports is introduced into the first inflation portion before the second inflation portion. The apparatus further includes a thickness limiting portion located between the first inflation portion and the second inflation portion and a tether. When the airbag is deployed and inflated, the thickness limiting portion limits the thickness of the airbag. The tether connects an upper end of the airbag and the thickness limiting portion to each other.