To provide a battery pack device which has a structure to envelop a battery cell by a tube for heat insulation and waterproofing in which the battery cells can be cooled efficiently.

The battery pack device includes a housing tube 15 which envelops a battery cell 11, a case 20 which houses a plurality of battery cells 11 enveloped by the housing tube 15, a fan 30 which circulates a heat exchange medium in the case 20 and cools the battery cells 11, a current sensor which detects at least one of current of charge and discharge to the battery pack 10, and a control device which has a calculation part to calculate the drive amount of the fan 30 corresponding to the detection value from the current sensor and an instruction part to instruct the drive amount to the fan 30 by delaying by a thermal transmission time portion of the housing tube 15.