Provided is a hydrotreating step (A) containing a hydroisomerization step (A1) that obtains a hydroisomerized oil (a1) by bringing a FT synthesis oil into contact with a hydroisomerization catalyst and/or a hydrocracking step (A2) that obtains a hydrocracked oil (a2) by bringing it into contact with a hydrocracking catalyst, and a fractionation step (B) that transfers at least a portion of the hydrotreated oil (a) composed of the hydroisomerized oil (a1) and/or the hydrocracked oil (a2) to a fractionator and, at the very least, obtains a middle distillate (b1) with a 5% distillation point of 130 to 170° C. and a 95% distillation point of 240 to 300° C., and a heavy oil (b2) that is heavier than the middle distillate (b1).