A porosity X of a positive electrode mixture layer 223 of a secondary battery 100 is 30(%)≦X. A mass ratio α of a positive electrode active material 610 in the positive electrode mixture layer 223 is 0.84≦α≦0.925 and a mass ratio β of a conductive material 620 in the positive electrode mixture layer 223 is 0.06≦β≦0.12. In the secondary battery 100, an index Y worked out from an expression below is 30 (mL/100 g)≦Y≦89 (mL/100 g). The index Y is given by the expression below, Y=A×α+B×β; where A is a DBP absorption number (mL/100 g) in the positive electrode active material 610; α is the mass ratio of the positive electrode active material 610 in the positive electrode mixture layer 223; B is a DBP absorption number (mL/100 g) of the conductive material 620; and β is the mass ratio of the conductive material 620 in the positive electrode mixture layer 223.