In 1995, the Environmental Agency prescribed an environmental quality standard for conventional railway noise. The standard is applied to newly-constructed lines and largely-remodelled lines to estimate the noise by use of equivalent sound level. The equivalent sound level is a time-averaged noise level. We proposed a noise prediction method for narrow-gauge railways, by which we can estimate the equivalent sound level. In this method, we divide the conventional railway noise into three components, rolling noise, motor-fan noise and concrete structure noise. The motor-fan noise is generated by the fans to cool driving motors. In order to confirm this method, we compared predicted noise levels with those measured on actual railways. As a result, we obtained the following conclusions. (1) The predicted noise levels tend to be slightly higher than actual noise levels, because we set the power level of motor-fan noise slightly higher. (2) The sound source models used in this method satisfactorily simulate the actual power level of rolling noise and structure noise.