It is investigated that in what shape the stress concentration factor of a notched strip under pure bending changes due to unsymmetrically varying notch angle. Four models made of CR-39, having parameters of r/d-0.225, h/r=4; r/d=0.225, h/r=2; r/d=0.4, h/r=4 and r/d=0.4, h/r=2 respectively as shown in Fig.1, Fig.2 and Table are tested with the use of polariscope. For each model, notch angle is unsymmetrically varied from $0^{circ}$ to $180^{circ}$ at intervals of $15^{circ}$ as shown in Fig. 1 and Fig. 2. The results of this experiment are Fig. 7 and Fig. 8 and the following are deduced. As notch angle increases 1) from $0^{circ}$ to $50^{circ}$, the decrement of concentration factor is slight. 2) from $50^{circ}$ to 90, the decrement of concentration factor is a little steeper. 3) from $30^{circ}$ to $140^{circ}$, the decrement of concentration factor is slight. 4) from $140^{circ}$ to $180^{circ}$, the decrement is very steep with an abrupt with an abrupt change in the neighborhood of $140^{circ}$.