Means for effecting rapid mass spectrometry of a multiplicity of samples; and a method of rapidly analyzing biosubstances such as nucleic acids and proteins. The above means is a solid support provided with a carbon layer onto which substances separated by gel electrophoresis are transferred. The above method is one for mass spectrometry of multiple substances which comprises separating substances of a sample by gel electrophoresis, transferring separated substances of the gel onto the above solid support so as to immobilize the same and subjecting the immobilized substances to desorption/ionization.