An electricity storage device includes a first battery stack (15), a second battery stack (11 to 14), and a case (22) that accommodates the first battery stack and the second battery stack. Each of the first battery stack and the second battery stack includes a plurality of cells (151) that are aligned and the second battery stack is placed under the first battery stack. The supporting member (80) that supports the first battery stack is placed between the first battery stack and the second battery stack and is fixed to the case.