The present invention pertains to a method for introducing a substance into a plant. This method includes the following steps: acquiring an enzyme-treated fertilized egg cell by (1-i) isolating, from a tissue containing a fertilized egg cell of a plant, the fertilized egg cell, and then performing a low titer condition treatment on the fertilized egg cell by an enzyme solution containing a plant tissue degrading enzyme, (i-11) performing a low titer condition treatment on a tissue containing a fertilized egg cell of a plant by an enzyme solution containing a plant tissue degrading enzyme, and then isolating the enzyme-treated fertilized egg cell, (1-iii) performing a low titer condition treatment on a tissue containing a fertilized egg cell of a plant by an enzyme solution containing a plant tissue degrading enzyme, and at the same time, isolating the enzyme-treated fertilized egg cell, (1-iv) isolating an egg cell and a sperm cell from a plant body and fusing the cells to produce a fertilized egg, and then p
