A time-of-flight mass spectrometer in which ions are accelerated and introduced into a flight space, and in which the ions are detected after being separated according to their mass-to-charge ratios while flying in the flight space, the time-of-flight mass spectrometer having a grid-like electrode for creating an electric field for accelerating and/or decelerating the ions in the direction along the thickness of the grid-like electrode while allowing the ions to pass through, characterized in that: the grid-like electrode is a structure having a thickness equal to or greater than two times a size of a smaller dimension of openings of the grid-like electrode, the thickness being the depth of the openings of the grid-fike electrode; or the grid-like electrode is a grid-like structure created by stacking a plurality of electrically conductive plates, with electrically conductive spacer members placed in between, to form an integrated body and by cutting this body at each of a plurality of planes (114, 115) orthogonal to the electrically conductive plates and arranged at predetermined intervals, the grid-like structure having openings whose width corresponds to a thickness of the electrically conductive spacer members and crosspieces whose width corresponds to a thickness of the electrically conductive plates, the crosspieces having a thickness corresponding to the interval of the cutting; or the grid-like electrode is a grid-like structure created by stacking a plurality of electrically conductive plates, with electrically conductive spacer members placed in between, to form an integrated body, the grid-like structure having openings whose width corresponds to the thickness of the electrically conductive spacer members and crosspieces whose width corresponds to the thickness of the electrically conductive plates, the crosspieces having a thickness corresponding to a size of one side of the electrically conductive plates. the grid-like electrode is a structure having a thickness equal to or greater than two times a size of a smaller dimension of openings of the grid-like electrode, the thickness being the depth of the openings of the grid-fike electrode; or the grid-like electrode is a grid-like structure created by stacking a plurality of electrically conductive plates, with electrically conductive spacer members placed in between, to form an integrated body and by cutting this body at each of a plurality of planes (114, 115) orthogonal to the electrically conductive plates and arranged at predetermined intervals, the grid-like structure having openings whose width corresponds to a thickness of the electrically conductive spacer members and crosspieces whose width corresponds to a thickness of the electrically conductive plates, the crosspieces having a thickness corresponding to the interval of the cutting; or the grid-like electrode is a grid-like structure created by stacking a plurality of electrically conductive plates, with electrically conductive spacer members placed in between, to form an integrated body, the grid-like structure having openings whose width corresponds to the thickness of the electrically conductive spacer members and crosspieces whose width corresponds to the thickness of the electrically conductive plates, the crosspieces having a thickness corresponding to a size of one side of the electrically conductive plates.