In order to estimate the confidence level of the velocity distribution shown in a velocity image reconstructed from a travel-time tomography, the ray coverage and the inversion characteristics of the system matrix were investigated. The targets of the analysis is the first arrival travel-time, the raypath information, and the resulting velocity model. The ray coverage, degree of ray and model coupling, was estimated by the number of rays and total ray length in a velocity grid, and information regarding the resolution and uncertainties involved in the reconstructed velocity model was derived from the results of the SVD analysis of the system matrix that relates the data space (first arrival travel times) to the model space (velocity distribution in tomogram).