The developing roller includes an electro-conductive substrate and a covering layer on the electro-conductive substrate, the covering layer including a matrix and an electro-conductive particle dispersed in the matrix, an arithmetic mean value of the current value is 300 pA or less and the standard deviation of the current value is 0.1-fold or less of the current value, a standard deviation of a potential is 3.0 V or more, and an arithmetic mean value of a volume resistivity is 1010 Ω·cm or less, and a standard deviation of the volume resistivity is 1-fold or more of the arithmetic mean value of the volume resistivity.