A curtain airbag device placement structure has an airbag module that is structured to include a curtain airbag folded-up in an elongated shape and an inflator supplying gas to the curtain airbag at a time of a side collision or the like, and that is assembled in advance to a top surface of a side terminal portion of a roof head lining. The inflator is disposed directly above a center pillar, and a pair of front and rear mounting leg portions of an inflator mounting bracket for fixing the inflator to a vehicle body are extended further toward a vehicle lower side than the side terminal portion of the roof head lining, and further, the inflator mounting bracket is fixed to the center pillar at the mounting leg portions.