To provide a fixing/releasing mechanism of a pendulum support device simple in structure and high in safety.

This fixing/releasing mechanism is constituted to make a clamping member 24 pressure contact with a holding member 22 through a spherical member 20 by providing a compression spring member 40 between a support plate 34 of a connecting shaft 30 of this pendulum support device and the clamping member 24, connecting a head end of a movable shaft 44 or a connecting shaft 46 of this actuator 42 by arranging the actuator 42 between the support plate 34 and a fixed plate 36, fixing a support shaft 20a by making the clamping member 24 pressure contact with the holding member 22 with the spherical member 20 by resiliency of the compression spring member 40 at the time when the actuator 42 is not energized and separating the clamping member 24 from the holding member 22 against resiliency of the compression spring member 40 when the actuator 40 is energized.