An expansion tank, while maintaining gas-liquid separation performance of coolant circulating through an engine cooling apparatus, can absorb pressure variations occurring with volume change of the coolant even when an excessive amount of coolant is supplied. A bulkhead 42 partitions an expansion tank 30 into separate chambers R1 to R6 that communicate with each other via a first communication hole 44 positioned lower than a FULL line. The separate chambers R4 to R6 that constitute a separate chamber group X communicate with each other via a third communication hole 45a positioned higher than the FULL line. The separate chambers R1 to R3 that constitute a separate chamber group Y communicate with each other via a fourth communication hole 45b positioned higher than the FULL line. The separate chamber R1 and the separate chamber R4 communicate with each other via a second communication hole 45c disposed at the height of the FULL line.
