A side airbag device includes: a side airbag in a folded state; a gas generator that includes an attachment portion to be attached to a vehicle, and that is configured to generate inflation gas to be supplied to the side airbag; a wrapping sheet that covers peripheries of the side airbag and the gas generator, and that is breakable when the side airbag is deployed and inflated; and a wire harness that includes a connection end portion electrically connected to the gas generator, and that is led out to an outer portion of the wrapping sheet. The wire harness is provided with a first locking portion, and the wrapping sheet is provided with a second locking portion that is locked to the first locking portion.