Authors experimented on flow patterns, distribution of quantity, especially loss of head at a cross-branch section by flowing air-water mixtures into a horizontal branch pipe of 23.4 mm in dia. They carried out the investigation from the following two view-points : (1) ξ_b1, loss of energy attributable to the branch only. (2) ξ_b2, loss of energy including the effect of the irregularity of the stream past a branch section. In consequence, it was possible for them to make the characteristics of the loss of energy comparatively clear. Then they discovered that the coefficient of loss of head ξ_b2' was approximately proportionate to the ratio of energy at the main flow and the branch flow.