A mounting structure for a curtain airbag device, the mounting structure comprising: a first pillar constituting a part of a front pillar and extending along a vehicle upper-lower direction; a second pillar constituting another part of the front pillar, disposed on a vehicle rear side at a predetermined interval with respect to the first pillar, and extending along the vehicle upper-lower direction; a transparent member interposed between the first pillar and the second pillar and allowing an outside of a vehicle to be visually recognized from a driver's seat side; a front pillar garnish covering the first pillar and the second pillar from a vehicle cabin side and having a lower end portion protruding along at least one of a vehicle front-rear direction and a vehicle width direction; a curtain airbag device configured to include a curtain airbag and being stored along the second pillar, the curtain airbag being configured to be able to be inflation-deployed in a curtain shape in a vehicle cabin side portion by receiving gas supply during a vehicle collision, and having a front end portion fixed at a position in the first pillar or the second pillar corresponding to the lower end portion of the front pillar garnish, characterized in that the front end portion of the curtain airbag is fixed at a position in the second pillar corresponding to the lower end portion of the front pillar garnish, in that the front pillar garnish includes: a front side garnish attached to the first pillar; and a rear side garnish configured as a body separate from the front side garnish, attached to the second pillar, covering the curtain airbag from a vehicle cabin inner side, and configured to be able to hold the curtain airbag in a state where the curtain airbag is apart from the second pillar, the rear side garnish being attached to the second pillar via a tether clip, and in that the rear side garnish has a body portion extending in the substantially vehicle upper-lower direction along the second pillar and an extending portion integrally formed with the vehicle upper side of the body portion, the vehicle upper side end portion of the extending portion abuts against the roof head liner, and the vehicle front side end portion of the extending portion is assembled to overlap an assembly portion, which is formed in the upper end portion of the front side garnish, from the vehicle cabin side. a first pillar constituting a part of a front pillar and extending along a vehicle upper-lower direction; a second pillar constituting another part of the front pillar, disposed on a vehicle rear side at a predetermined interval with respect to the first pillar, and extending along the vehicle upper-lower direction; a transparent member interposed between the first pillar and the second pillar and allowing an outside of a vehicle to be visually recognized from a driver's seat side; a front pillar garnish covering the first pillar and the second pillar from a vehicle cabin side and having a lower end portion protruding along at least one of a vehicle front-rear direction and a vehicle width direction; a curtain airbag device configured to include a curtain airbag and being stored along the second pillar, the curtain airbag being configured to be able to be inflation-deployed in a curtain shape in a vehicle cabin side portion by receiving gas supply during a vehicle collision, and having a front end portion fixed at a position in the first pillar or the second pillar corresponding to the lower end portion of the front pillar garnish, the front end portion of the curtain airbag is fixed at a position in the second pillar corresponding to the lower end portion of the front pillar garnish, in that the front pillar garnish includes: a front side garnish attached to the first pillar; and a rear side garnish configured as a body separate from the front side garnish, attached to the second pillar, covering the curtain airbag from a vehicle cabin inner side, and configured to be able to hold the curtain airbag in a state where the curtain airbag is apart from the second pillar, the rear side garnish being attached to the second pillar via a tether clip, a front side garnish attached to the first pillar; and a rear side garnish configured as a body separate from the front side garnish, attached to the second pillar, covering the curtain airbag from a vehicle cabin inner side, and configured to be able to hold the curtain airbag in a state where the curtain airbag is apart from the second pillar, the rear side garnish being attached to the second pillar via a tether clip, and in that the rear side garnish has a body portion extending in the substantially vehicle upper-lower direction along the second pillar and an extending portion integrally formed with the vehicle upper side of the body portion, the vehicle upper side end portion of the extending portion abuts against the roof head liner, and the vehicle front side end portion of the extending portion is assembled to overlap an assembly portion, which is formed in the upper end portion of the front side garnish, from the vehicle cabin side. the vehicle upper side end portion of the extending portion abuts against the roof head liner, and the vehicle front side end portion of the extending portion is assembled to overlap an assembly portion, which is formed in the upper end portion of the front side garnish, from the vehicle cabin side.