Subterranean termites live their tunnel networks constructed below ground. Thus, they often encounter tunnel junctions during traveling in the networks. Directional selection by termites at the junctions is likely to affect foraging efficiency because the selection determines the total traveling distance of the termites in the networks. To understand how termites select their direction at the junctions, we artificially constructed skewed T-junctions (with skew angle, θ = 0°, 10°, 20°, …, and 80°) in small arenas and observed termite behavior at the junctions. When an advancing termite touched the tunnel wall of a junction using left (right) antenna, the termite strongly tended to turn their body to the right (left) side. We measured the ratio of termite's directional selection for right side tunnel (γR). The ratio of the left selection was given as γL = 1 − γR. The value of γR tended to increase gradually as θincreased in the range of 0° ≤ θ ≤ 70° and dramatically decreased at θ = 80°. This experimental result was explained by the relationship between the antenna touching order and the geometry of junction area. Based on the selection behavior, we built a mathematical model and verified it through the comparison with experimental data. In addition, we briefly discussed about the application of the model and the selection mechanism in relation to the foraging efficiency.