Provided are a method for measuring tool dimensions and a measurement device, whereby if a machine tool (10) cannot fit the overall outline of a tool (20) inside the field of vision (V) for an image from an imaging device (33), the field of vision (V) of the imaging device (33) is moved by relatively moving the imaging device (33) and the tool (20). In addition, the imaging device (33) can follow the outline (54) of the tool (20) by moving the field of vision (V), because the movement direction (53) for the field of vision (V) is determined on the basis of the partial outline (51) specified based on image data. In this way, even when measuring dimensions for a tool (20) with a larger diameter than the field of vision (V) of the imaging device (33), a partial outline (51) of a desired range, for example, is specified. An outline of a desired range for the tool (20) is extracted if a plurality of specified partial outlines (51) are combined. Measurement of the dimensions of the tool (20) is possible by using such outlines.