A release-promoting agent is configured to be applied to a heating member in a fixing device that presses the heating member against a recording medium on which a toner image is formed and fixes the toner image to the recording medium, to promote release of the toner image from the heating member. The release-promoting agent is formed with a mixture of a dimethyl polysiloxane and an amino group-containing dimethyl polysiloxane represented by respectively, where b.noteq.0, and c>1000.