A manufacturing method for a motor core in which a magnet is fixed in a magnet accommodating portion using synthetic resin material includes: a fixing step of fixing the a permanent magnet in the a magnet accommodating portion using a synthetic resin material, wherein the fixing step includes: an injection step of setting a temperature of the synthetic resin material to a first temperature and injecting, with an injection device having a container capable of maintaining the synthetic resin material in the softened state, the softened synthetic resin material into the magnet accommodating portion; and a curing step of raising the temperature of the synthetic resin material injected into the stacked body to a second temperature to cure the synthetic resin material, with the injection device being moved away from the stacked body.