Provided is a highly reactive fluid fan clutch device excellent in reaction speed of fan rotation to a control signal even with a weak centrifugal force during low fan rotation. The device of an external control type includes: an annular oil reserving chamber provided in a case that is supported by a rotary shaft having a drive disk fixed thereto; and a valve member for opening and closing an oil circulating flow passage hole of the annular oil reserving chamber by an electromagnet, wherein an effective oil contact area at a torque transmission gap formed between a drive side and a driven side is increased and decreased to control rotation torque transmission from the drive side to the driven side, and an inner wall eccentric to an outer wall of the annular oil reserving chamber is provided in the annular oil reserving chamber.