Spectral properties of one-dimensional tungsten gratings with various depths and widths of grooves were investigated by means of finite-difference time-domain simulation with a multi-Lorentz model. Shallow gratings showed a strong absorption peak due to surface plasmon polaritons when the oscillation of the electric field was parallel to the grating vector. On the other hand, deep gratings with wide grooves showed a different absorption attributed to the microcavity effect when the oscillation of the electric field was perpendicular to the grating vector. With narrowed grooves, another absorption with d-dependence occurred, which was probably due to vertically oscillating surface plasmons to the grooves.