NOVELTY - A positive electrode active material component (10) has reaction suppressing portion (2) containing oxide and covering surface of oxide-based active material (1). Ratio of metallic element contained in active material corresponding to etching amount (E) (in nm) of silicon oxide conversion is set to M1. Ratio of element other than oxygen contained in oxide of reaction suppressing portion is set to M2. A curve is drawn by setting etching amount (E) as X-axis and ratio (M2/(M1+M2)) as Y-axis. Value of linear inclination in drop portion of curve is 0.02 or less.    USE - Positive electrode active material component is used for solid-state battery (claimed) used as power supply for personal computer, video camera, mobile telephone, communication apparatus and electric vehicles.    ADVANTAGE - The increase in interfacial resistance of oxide-based positive electrode active material and electrolyte material is suppressed even at high temperature.    DETAILED DESCRIPTION - A positive electrode active material component has a reaction suppressing portion containing oxide and covering the surface of oxide-based positive electrode active material. The ratio (in mol%) of metallic element (excluding metallic element used as conductive ion) contained in active material corresponding to etching amount (E) (in nm) of silicon oxide conversion measured based on X-ray photoelectron spectroscopy (XPS) measurement with depth analysis is set to M1. The ratio of (in mol%) of element other than oxygen contained in oxide of reaction suppressing portion is set to M2. A curve is drawn by setting etching amount (E) as X-axis and ratio (M2/(M1+M2)) as Y-axis. The value of linear inclination in sudden drop portion of curve is 0.02 or less. INDEPENDENT CLAIMS are included for the following:    (1) solid-state battery; and    (2) manufacture of positive electrode active material component.    DESCRIPTION OF DRAWING(S) - The drawing shows the sectional view of positive electrode active material.    Oxide-based positive electrode active material (1)    Reaction suppressing portion (2)    Positive electrode active material component (10)