Energy storage unit and the power storage system

A voltage or remaining capacity between the power storage units, in order to equalize while suppressing an increase in circuit size and cost, in the energy storage unit (10), a voltage detection circuit (14), a plurality of series-connected cells (Vc1- VC8) voltage to detect the. Voltage detection circuit (14) is supplied with power supply voltage from both ends of the plurality of cells (VC1-VC8). DC-DC converter (15) converts the voltage across the plurality of cells (VC1-VC8) to another DC voltage (VCC). Adjusting circuit (16) adjusts the power consumption of a plurality of cells (VC1-VC8). Adjusting circuit (16) operates the generated DC voltage (VCC) as a power supply voltage by the DC-DC converter (15).