To solve the problem of heat radiation from a vibration mitigation device and the problem of oil leakage resulting from prolonged use thereof when a device for converting vibration generated by vertical movement of wheels of a land traveling vehicle to electric power is installed around and along with the vibration relaxation device.

An air circulation space 28 is placed around a periphery of a vibration mitigation device, an inner wall of a generator is placed outside the same, and air is circulated through the same by vertical movement of an upper skeleton holding unit 2; fins are placed on a periphery of a vibration control device to lower the temperature thereof with circulated air; and oil leaked through the air circulation space 28 is discharged outside of a system.