The present invention aims to provide a binder for a power storage device electrode which exhibits thermal energy stability over a wide temperature range covering from a high-temperature condition to a low-temperature condition when used as a binder for a power storage device electrode, and which enables production of a high-capacity storage battery with a small irreversible capacity and low resistance to have excellent output characteristics. The present invention also aims to provide a binder for a power storage device electrode which is excellent in dispersibility of an active material and adhesiveness, which improves the flexibility of an electrode to be obtained, and which has high resistance against electrolytes to enable production of a high-capacity storage battery even when the added amount thereof is small. The present invention further aims to provide a composition for a power storage device electrode, a power storage device electrode, and a power storage device each prepared using the binder for a power storage device electrode. The present invention relates to a binder for a power storage device electrode used for an electrode of a power storage device, the binder including a polyvinyl acetal resin, the polyvinyl acetal resin having a meso/racemo ratio of an acetal ring structure of 10 or higher and a hydroxy group content of 30 to 60 mol%.