An actuator which is adapted to be mounted on a first mounting region and on a second mounting region so as to be operable to separate the second mounting region from the first mounting region, the actuator comprising a housing section that houses a driving source and is adapted to be mounted on the first mounting region and a deploying section that is adapted to be mounted on the second mounting region and deployable, when pressed by a driving force of the driving source, in such a fashion as to move forward relative to the housing section and to separate the second mounting region from the first mounting region, wherein the housing section comprises: a case that is tubular and formed from metal; a securing member that is disposed inside the case and secured to the case for supporting the driving source; and a mounting hole that is used to mount the housing section on the first mounting region, the mounting hole being formed in a direction perpendicular to an axial center of the case for receiving a pivot member connected to the first mounting region, characterized in that: the mounting hole is formed at a root end region of the housing section, which root end region being disposed on an opposite side to a deploying direction of the deploying section with respect to the driving source; the mounting hole is composed of a mounting hole formed in the case and a mounting hole formed in the securing member, thus the mounting hole is formed in such a manner as to penetrate the case and securing member, the housing section further comprises a fixing hole (41, 62a) for receiving a fixing member that fixes the securing member to the case and prevents disengagement of the securing member from the case in an opposite direction to the deploying direction of the deploying section; the fixing hole (41, 62a) is formed through the case and the securing member in a direction perpendicular to the axial center of the case and is disposed at a different position from the mounting hole (40a, 62b) in the root end region of the housing section; and an inner circumferential plane of the mounting hole of the case is configured to be brought into contact with the pivot member at least on a region thereof disposed towards the deploying direction of the deploying section when the actuator is actuated. a case that is tubular and formed from metal; a securing member that is disposed inside the case and secured to the case for supporting the driving source; and a mounting hole that is used to mount the housing section on the first mounting region, the mounting hole being formed in a direction perpendicular to an axial center of the case for receiving a pivot member connected to the first mounting region, characterized in that: the mounting hole is formed at a root end region of the housing section, which root end region being disposed on an opposite side to a deploying direction of the deploying section with respect to the driving source; the mounting hole is composed of a mounting hole formed in the case and a mounting hole formed in the securing member, thus the mounting hole is formed in such a manner as to penetrate the case and securing member, the housing section further comprises a fixing hole (41, 62a) for receiving a fixing member that fixes the securing member to the case and prevents disengagement of the securing member from the case in an opposite direction to the deploying direction of the deploying section; the fixing hole (41, 62a) is formed through the case and the securing member in a direction perpendicular to the axial center of the case and is disposed at a different position from the mounting hole (40a, 62b) in the root end region of the housing section; and an inner circumferential plane of the mounting hole of the case is configured to be brought into contact with the pivot member at least on a region thereof disposed towards the deploying direction of the deploying section when the actuator is actuated. the mounting hole is formed at a root end region of the housing section, which root end region being disposed on an opposite side to a deploying direction of the deploying section with respect to the driving source; the mounting hole is composed of a mounting hole formed in the case and a mounting hole formed in the securing member, thus the mounting hole is formed in such a manner as to penetrate the case and securing member, the housing section further comprises a fixing hole (41, 62a) for receiving a fixing member that fixes the securing member to the case and prevents disengagement of the securing member from the case in an opposite direction to the deploying direction of the deploying section; the fixing hole (41, 62a) is formed through the case and the securing member in a direction perpendicular to the axial center of the case and is disposed at a different position from the mounting hole (40a, 62b) in the root end region of the housing section; and an inner circumferential plane of the mounting hole of the case is configured to be brought into contact with the pivot member at least on a region thereof disposed towards the deploying direction of the deploying section when the actuator is actuated.