The magnetic field dependences of the thermoelectric effect, the magnetoresistance, the thermal conductivity and the transverse Nernst-Ettingshausen effect are investigated on Bi₈₈Sb₁₂ alloy single crystals. The Seebeck effect under the magnetic field along the temperature gradient is the longitudinal Nernst-Ettingshausen effect. The longitudinal and transverse Nernst-Ettingshausen effects (LNE and THE respectively) have been measured with the magnetic field up to 1.2T and at the temperature of 100K to 300K. Two configurations, B_z//c-axis and B_z⊥ c-axis, have been used. The Seebeck coefficient of the minus sign increases in the absolute value as the temperature is lowered. By the application of the magnetic field, the coefficient very much increases in the minus sense. The increase of the resistivity by the magnetic field is more drastic compared to the increase of Seebeck effect. The magnetic field dependence of the thermal conductivity κ is minor compared to the Seebeck effect S and the magnetoresistivity ρ_B. The figure of merit Z (=S²/ρ_Bκ) is calculated by using the measured values of S, ρ_B and κ. Z value without the field changes from 5×10^-4K^-1 at 300K to 4×10^-3K^-1 at 110K. By applying the field of 1.2T, Z-value increase about 20-30% above about 160K, while decreases down to 5×10^-4K^-1 at 110K. The addition of an appropriate impurity such as Te should improve the Z under the magnetic field. The merit of the TNE effect for the thermomagnetic application is mentioned.