Tapered end mills are indispensable cutters for machining of inclined surface with conventional type of numerical controlled machine tools, for instance side surface of mold and die. But, the cutter deflection problem of tapered end mills has not been analized. This paper therefore tries to analyze cutter deflection by statical load based on flexural rigidity of cutter and aims at presenting basic data on tool design and improvement of cutting method. The main results are as follows: (1) Flexural rigidity and equivalent diameter of tapered end mill are calculated by cross-sections of the tool. And the model consists of truncated cones is generated in order to calculate a deflection of the tapered end mill. (2) Calculating method of deflection of the center axis of the truncated cones model by statical load are shown. (3) Deflection curve of the cutter axis by statical load on end of the tool is calculated, and obtained following results. (i) In case of 4 teeth, the maximum deflection of the tool for one-half of tapered angle α=2° is smaller than that for α=3°. But the maximum values of tapered end mills are about 35% for α=2° and 29% for a=3°greater than that of assumed square end mills. (ii) In case of 2 teeth, the deflection changes depend on the direction of load, and maximum value is about 1.5 times the minimum value. But the range of fluctuation of deflection decreases about one-half for α=2° and 3° with increase of helix angle from 24° to 45° respectively.