for the above described substance containing an acid to be crystallized and become a matrix material for a protein even if the substance containing an acid remains in a sample the mass spectrum of the acid does not correspond to that of the target object because each of the above listed acids has a relatively low molecular weight meanwhile all the above listed acids have no aromatic rings and hardly absorb laser beams such as nitrogen laser beams so that extra ions are not generated even when the laser beams are used as excitation beams in the present invention a substrate where a protein to be analyzed is arranged is preferably a gold substrate or a substrate obtained by applying a gold film onto the surface of the substrate however it is not particularly limited and may be applied to a protein tip including a conducting substrate such as a silicon substrate and an insulating substrate such as an organic polymer or glass as long as the substance of the substrate generates no secondary ion that has mass to prevent obtaining mass information of the protein furthermore a media where a protein to be analyzed is arranged is not limited by the shape of the substrate and there may be used solid substances having any shape such as powder and granular shapes information about the mass of a target object or a component thereof in the present invention is the information about the mass of either 1 an ion corresponding to the mass number of.