NOVELTY - The negative electrode active material has a porous carbon material that is provided with open-holes (12) connected to a surface (11), closed pores (13) not connected to the surface, and a solid portion (14) consisting of carbon materials. The distance between the planes of solid portion is about 0.340-0.410 nm. A volume ratio rate of closed pores is about 0-10% of the volume sum of open-holes, closed pores and solid portion. A volume ratio rate of open-holes is about 0-50% of the volume sum of closed pores, open-holes and the solid portion.    USE - Negative electrode active material for sodium ion secondary battery (claimed) used for power supply of portable electronic device, electrical storage device for electric power leveling used with power generation equipments such as thermal power generation, wind power generation and fuel cell power generation equipments, power supply of general household, emergency electrical storage system for collective-housing, off-peak electric power electrical storage system, Uninterruptible power supply (UPS), and power supply of transporting apparatus such as electric vehicle, hybrid vehicle, and plug-in hybrid motor vehicle.    ADVANTAGE - The negative electrode active material provided for sodium ion secondary batteries is provided with a large capacitance per unit volume, so that high capacitance sodium ion secondary battery is manufactured efficiently. The negative reversible reaction which arises on the open-hole surface is inhibited. The efficiency of negative electrode active material is improved.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a sodium ion secondary battery; and    (2) a manufacturing method of negative electrode active material for sodium ion secondary batteries.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of the negative electrode active material for sodium ion secondary battery.    Surface (11)    Open-hole (12)    Closed pore (13)    Solid portion (14)