1. A three-dimensional skeleton data compression apparatus for compressing and holding skeleton data, used in a three-dimensional polygon display apparatus that renders a three-dimensional character described by polygon data and skeleton data, comprising: a weight detecting part for detecting weight information that is a numerical value representing a relationship between a skeleton and a polygon vertex and showing a degree of an influence of movement of the skeleton on the vertex, based on input skeleton data; a weight compression threshold value setting part for setting a weight compression threshold value that is set by a user and used for deleting weight information equal to or lower than the numerical value as the weight information having a small degree of an influence involved in the movement of the skeleton; and a weight compressing part for reducing/compressing weight information equal to or lower than the set weight compression threshold value, among weight information detected by the weight detecting part.