A surgical instrument holding device comprising: a holding body that has a first engagement receiving portion; a separator that has a second engagement receiving portion and that is detachable from the holding body; an adapter that is detachable from the separator and from which a surgical instrument is detachable; and a driving body configured to support the holding body in a rotatable manner and apply a driving force to the holding body, characterized in that the separator is provided with a first engaging portion that is elastically deformed and engaged with the first engagement receiving portion at a time of attachment of the separator to the holding body, the adapter is provided with a second engaging portion that is elastically deformed and engaged with the second engagement receiving portion at a time of attachment of the adapter to the separator, and the separator is attached to the holding body by engagement of the first engaging portion with the first engagement receiving portion in a state in which the first engaging portion is elastically restored, and the adapter is attached to the separator by engagement of the second engaging portion with the second engagement receiving portion in a state in which the second engaging portion is elastically restored, wherein the adapter is provided with a deformation restricting portion configured to restrict deformation of the first engaging portion in a state in which the adapter is attached to the separator, and, in a state in which the separator is attached to the holding body, the deformation restricting portion restricts the deformation in a direction in which the engagement of the first engaging portion with the first engagement receiving portion is cancelled. a holding body that has a first engagement receiving portion; a separator that has a second engagement receiving portion and that is detachable from the holding body; an adapter that is detachable from the separator and from which a surgical instrument is detachable; and a driving body configured to support the holding body in a rotatable manner and apply a driving force to the holding body, characterized in that the separator is provided with a first engaging portion that is elastically deformed and engaged with the first engagement receiving portion at a time of attachment of the separator to the holding body, the adapter is provided with a second engaging portion that is elastically deformed and engaged with the second engagement receiving portion at a time of attachment of the adapter to the separator, and the separator is attached to the holding body by engagement of the first engaging portion with the first engagement receiving portion in a state in which the first engaging portion is elastically restored, and the adapter is attached to the separator by engagement of the second engaging portion with the second engagement receiving portion in a state in which the second engaging portion is elastically restored, wherein the adapter is provided with a deformation restricting portion configured to restrict deformation of the first engaging portion in a state in which the adapter is attached to the separator, and, in a state in which the separator is attached to the holding body, the deformation restricting portion restricts the deformation in a direction in which the engagement of the first engaging portion with the first engagement receiving portion is cancelled.