PROBLEM TO BE SOLVED: To provide a Si-based alloy negative electrode material having excellent conductivity and an electrode using the same of a power storage device accompanied with moving of lithium ions at charging and discharging, such as a lithium ion secondary battery, a hybrid capacitor, an all-solid lithium ion secondary battery, and the like.SOLUTION: Provided is a negative electrode material formed of an Si-based alloy for power storage devices accompanied with moving of lithium ions at charging and discharging, in which the negative electrode material formed of the Si-based alloy has a Si primary phase made of Si and a compound phase made of Si and at least one kind of elements other than Si, the compound phase has a phase containing a phase made of Si and Cu, and Si crystallite size of the Si primary phase is 30nm or less and a crystallite size of the compound phase made of Si and Cu is 40nm or less.
