NOVELTY - A bipolar secondary battery (10) consists of cell layer(s) (19) having positive-electrode active-material layer (13) formed on collector (11), electrolyte layer (17) laminated on positive-electrode active-material layer, and a negative-electrode active-material layer (15) formed on other surface of collector. The weight decrease amount of the electrolyte when left still at a pressure of 10 Torr and a temperature of 25 degrees C for 1 hour is 1 %mass or less with respect to the mass of electrolyte before leaving.    USE - Bipolar secondary battery e.g. bipolar type lithium ion secondary battery is used for producing assembled batteries used in vehicles (all claimed) e.g. hybrid vehicles and electric vehicles e.g. car (from drawings).    ADVANTAGE - The bipolar secondary battery has excellent reliability and durability, and suppressed gas evolution.    DETAILED DESCRIPTION - A bipolar secondary battery consists of an electric-power generation element (21) in which a seal portion (31) is formed at the outer peripheral portion of cell layer(s). The cell layer consists of a bipolar type electrode comprising a positive-electrode active-material layer formed on one surface of a collector, an electrolyte layer containing an electrolyte laminated on the positive-electrode active-material layer, and a negative-electrode active-material layer formed on the other surface of collector. The weight decrease amount of the electrolyte when left still at a pressure of 10 Torr and a temperature of 25 degrees C for 1 hour is 1 %mass or less with respect to the mass of electrolyte before leaving. An INDEPENDENT CLAIM is included for manufacture of bipolar secondary battery, which involves preparing a bipolar type electrode and an electrolyte, laminating the electrode, and electrolyte layer or its precursor, to obtain a laminate (29) consisting of a cell layer, forming a seal portion at the outer peripheral portion of cell layer, and carrying out pressure-reduction process of the electrolyte at less than 10 Torr before or simultaneously with seal-portion formation.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional schematic view of the bipolar secondary battery.    Bipolar secondary battery (10)    Collector (11)    Positive-electrode active-material layer (13)    Negative-electrode active-material layer (15)    Electrolyte layer (17)    Cell layer (19)    Electric-power generation element (21)    Laminate (29)    Seal portion (31)