First-principles calculations were employed to evaluate the trapping energy of a H atom in a screw dislocation and an edge dislocation in Al. After obtaining the dislocation core structure in the absence of H, we calculated the trapping energy of H at several tens of possible trapping sites in the dislocation core and its vicinity. The maximum trapping energies were 0.08 and 0.15 eV/atom for the screw and edge dislocations without the zero-point vibrational energy correction, while they were 0.11 and 0.18 eV/atom for the screw and the edge dislocations with the correction. The calculation conditions employed in the present work correspond to the line density of approximately 1.0 H atom/nm along the dislocation line, which is sufficiently low to exclude H-H interaction.