A cultured cell of Rhaphiolepis umbellata Thunb. having high differentiating power, said cultured cell being obtained by culturing a part of a tissue of the Rhaphiolepis umbellata Thunb. in a culture medium containing benzyladenine and naphthaleneacetic acid (NAA) in an amount effective to induce callus formation of the Rhaphiolepis umbellata Thunb.