A nickel-metal hydride storage battery is provided capable of suppressing an increase of discharge reserve of a negative electrode and preventing lowering of battery characteristics. A nickel-metal hydride storage battery 100 of the present invention comprises a battery main part (an electrode plate group 150, an electrolyte, and others), a case 102 housing this battery main part, and a safety valve device 101 having an excessive pressure preventing function for preventing excessive rise of the internal pressure in the case 102 by discharging gas from the case 102 when the internal pressure in the case 102 exceeds a predetermined value. The safety valve device 101 includes a valve member 110 having a protruding wall 118 forming a valve internal space C communicated with a release hole 122 and has a hydrogen leakage function for allowing leakage of hydrogen gas in the case 102 out of the battery through the valve internal space C even when the internal pressure in the case 102 is the predetermined value or less.