[Object] It is an object to provide an injection method for injecting an electrolyte and an electrolyte injection apparatus which allow the electrolyte to be injected and filled into an electrode assembly within an outer can with favorable permeation, thereby easily manufacturing an electrolyte secondary battery having favorable cycle characteristics at good yield.[Solution] A solution injection nozzle 10 is inserted into a solution injection hole 101 of an outer can 100 in which an electrode assembly 110 is stored, and the solution injection hole 101 is hermetically sealed by a pressure reducing pad 11 provided so as to surround a periphery of the solution injection nozzle 10. An inside of the outer can 100 is made into a negative pressure through the pressure reducing pad 11, and an electrolyte L is supplied from the solution injection nozzle 10 into the outer can 100. The outer can 100 is rotated with the solution injection nozzle 10 as a rotation center.