A curtain airbag device mounting structure comprising: a first pillar that forms a part of a front pillar and extends substantially along a vehicle height direction; a second pillar that forms another part of the front pillar, the second pillar being disposed on a rear side of a vehicle relative to the first pillar at a predetermined distance from the first pillar and extending substantially along the vehicle height direction; a transparent member that is bridged between the first pillar and the second pillar and enables an outside of the vehicle to be viewed from a driver seat; and a curtain airbag device including a curtain airbag stored along a roof side rail and the second pillar, the curtain airbag being configured to be supplied with gas to inflate and deploy in a curtain-like fashion over a side portion of a cabin of the vehicle in case of a collision of the vehicle, characterized in that a front pillar garnish is attached to a vehicle interior side of the front pillar, wherein the front pillar garnish includes a front-side garnish attached to the first pillar and a rear-side garnish formed separately from the front-side garnish and attached to the second pillar, the rear-side garnish being configured to cover the curtain airbag from a vehicle interior side of the curtain airbag and to hold the curtain airbag in a state in which the curtain airbag is apart from the second pillar, wherein the rear-side garnish is attached to the second pillar via a tether clip, and a portion of the rear-side garnish is laid on a portion of the front-side garnish. a first pillar that forms a part of a front pillar and extends substantially along a vehicle height direction; a second pillar that forms another part of the front pillar, the second pillar being disposed on a rear side of a vehicle relative to the first pillar at a predetermined distance from the first pillar and extending substantially along the vehicle height direction; a transparent member that is bridged between the first pillar and the second pillar and enables an outside of the vehicle to be viewed from a driver seat; and a curtain airbag device including a curtain airbag stored along a roof side rail and the second pillar, the curtain airbag being configured to be supplied with gas to inflate and deploy in a curtain-like fashion over a side portion of a cabin of the vehicle in case of a collision of the vehicle, characterized in that a front pillar garnish is attached to a vehicle interior side of the front pillar, wherein the front pillar garnish includes a front-side garnish attached to the first pillar and a rear-side garnish formed separately from the front-side garnish and attached to the second pillar, the rear-side garnish being configured to cover the curtain airbag from a vehicle interior side of the curtain airbag and to hold the curtain airbag in a state in which the curtain airbag is apart from the second pillar, a front-side garnish attached to the first pillar and a rear-side garnish formed separately from the front-side garnish and attached to the second pillar, the rear-side garnish being configured to cover the curtain airbag from a vehicle interior side of the curtain airbag and to hold the curtain airbag in a state in which the curtain airbag is apart from the second pillar, wherein the rear-side garnish is attached to the second pillar via a tether clip, and a portion of the rear-side garnish is laid on a portion of the front-side garnish.