Movable device, movable seat, and method for manufacturing movable device

[Solution] A movable device is provided with a holding body and a movable body. The holding body, which has a first opening and an internal space, is configured as a single component. The movable body has an internal body and a first movable shaft part. The internal body is accommodated in the internal space of the holding body, and is too large to be pulled out from the first opening even if the first opening elastically deforms. The first movable shaft part is configured to be capable of moving integrally with the internal body, and is configured so as to face out of the holding body from within the holding body through the first opening.