Abstract: A vuilleumier heat pump device comprises: a hot-side heat pump (2) in which a hot side displacer (22) is housed in a hot side cylinder (21); and a cold-side heat pump (3) in which a cold side displacer (32) is housed in a cold side cylinder (31). Rods (23, 33) respectively connected to the displacers (22, 32) are connected to each other through a connection mechanism (4). In the vuilleumier heat pump device, a volume of the cold side rod (33) in a middle-temperature space (35) is adjusted. In this case, a rotation speed of a crank shaft (42) of the connection mechanism (4) is detected, a volume of the rod in a middle-temperature space (35) according to the rotation speed is calculated, and then the volume of the cold side rod (33) in a middle-temperature space (35) is adjusted so as to reach the calculated volume of the rod.

Abstract: Coefficient of performance (COP.sub.L), (COP.sub.H) is lowered when cooling capability or heating capability (Qk) is increased by increasing a revolution speed (N) because an working gas temperature (Tc) of a cold space (9L) drops and an working gas temperature (Tm) of a middle-temperature spaces (10H), (10L) rises. In order to avoid the lowering thereof, a vuilleumier heat pump device is provided with sensors (26), (29) for respectively detecting the respective working gas temperatures (Tc), (Tm), adjusting means (27), (30) for increasing or decreasing heat input of an endothermic heat exchanger (23) of a heat input circuit (22) and heat output of a radiation heat exchanger (25) of a radiation circuit (24) respectively, and control means (28), (31) for controlling the respective adjusting means (27), (30) so as to increase the heat input and the heat output in accordance with rise or drop of the gas temperature (Tc), (Tm).