To easily perform a process for linear dot elements having a branch.

A branch detecting means 38 detects the branch point of linear array dot elements having the branch by pattern matching. A branch disconnecting means 40 disconnects the linear array dot elements at the detected branch point to separate the linear array dot elements having the branch into plural linear array dot elements having no branch. An element converting means 42 converts the linear array dot elements having no branch into straight lines. A connecting means 44 connects the converted straight lines together according to feature information on the straight lines to generate a new straight line. An image evaluating means 46 evaluates an image according to various statistics of straight lines within a specific range in an image space. Therefore, the image of fiber which is complicatedly entangled can easily be evaluated.