Ion optical grids are widely used to accelerate or decelerate ions in time-of-flight mass spectrometer (TOF-MS). This "real" grid has the following disadvantages: (a) ion loss on the grids, (b) divergence of ion trajectories due to lens action, and (c) low mechanical strength. To suppress the divergence, it is effective to reduce a pitch of grid . Parallel wire grids with 20-um wires at 250-um pitch are available, giving a transmission of 92 %. This kind of grids is especially suitable for ion refectors. On the other hand, fine electroformed meshes are used for orthogonal accelerators; however, thickness of the mesh is limited to typically 10 um by manufacturing reasons. If the extraction field inside the accelerator is increased to improve mass resolving power, mechanical strength is insufficient and these grids would be loosen or broken. It is therefore necessary to develop fine grids with high mechanical strength.