A method of measuring a taper angle in a wire electric discharge machining apparatus comprises, the steps of: providing a measuring tool (2) having lower and upper edges (27, 23) being spaced by a given height (H); moving a vertical wire electrode (EV) from a reference position (R) in one direction by a first distance (X1) to the lower edge (27); moving the vertical wire electrode from the reference position in the one direction by a second distance (X2) to the upper edge (23); moving an inclined wire electrode (EI) from the reference position in the one direction by a third distance (X3) to the lower edge; moving the inclined wire electrode from the reference position in the one direction by a fourth distance (X4) to the upper edge; and calculating a taper angle (θ) of the inclined wire electrode based on the following equation: θ=tan−1 γ/H γ=|(X3−X1)−(X4−X2)|.