An image drawing apparatus for drawing an object, which includes multiple polygons (202a, 202b) and has a changing transparency, in a frame buffer with reference to a Z-buffer, comprising: a change rate setting section for setting a transparency change rate of the object; a threshold setting section for setting a writing threshold used for determining whether a Z value of a view coordinate system (X', Y', Z') should be written to the Z-buffer in connection with each pixel where each of the multiple polygons (202a, 202b) is perspective-transformed from a viewpoint and projected on a virtual screen; a Z value calculating section for calculating the Z value in connection with each pixel and for each of the multiple polygons (202a, 202b) projected on the virtual screen; a transparency calculating section for calculating transparency in connection with each pixel included in a polygon according to the set transparency change rate; a transparency comparing section for comparing the calculated transparency of each pixel with the set writing threshold; a Z-buffer writing section for writing the calculated Z value of the pixel to the Z-buffer when the calculated Z-value is equal to or lower than a Z-value of the pixel of a polygon already processed written in the Z-buffer and the transparency is lower than the writing threshold; an image writing section for writing image data of each pixel of the polygon (202a, 202b) to the frame buffer when the calculated Z-value is equal to or lower than a Z-value of a pixel of the polygon already processed written in the Z-buffer; and a display control section for causing a display to display an image corresponding to image data written to the frame buffer; characterized in that said threshold setting section setting said writing threshold according to the transparency change rate set by said change rate setting section, such that said writing threshold is changed in the same way as said transparency change rate, and the relationship in size between said writing threshold and the calculated transparency of each pixel remains constant, when said transparency change rate is changed. a change rate setting section for setting a transparency change rate of the object; a threshold setting section for setting a writing threshold used for determining whether a Z value of a view coordinate system (X', Y', Z') should be written to the Z-buffer in connection with each pixel where each of the multiple polygons (202a, 202b) is perspective-transformed from a viewpoint and projected on a virtual screen; a Z value calculating section for calculating the Z value in connection with each pixel and for each of the multiple polygons (202a, 202b) projected on the virtual screen; a transparency calculating section for calculating transparency in connection with each pixel included in a polygon according to the set transparency change rate; a transparency comparing section for comparing the calculated transparency of each pixel with the set writing threshold; a Z-buffer writing section for writing the calculated Z value of the pixel to the Z-buffer when the calculated Z-value is equal to or lower than a Z-value of the pixel of a polygon already processed written in the Z-buffer and the transparency is lower than the writing threshold; an image writing section for writing image data of each pixel of the polygon (202a, 202b) to the frame buffer when the calculated Z-value is equal to or lower than a Z-value of a pixel of the polygon already processed written in the Z-buffer; and a display control section for causing a display to display an image corresponding to image data written to the frame buffer; characterized in that said threshold setting section setting said writing threshold according to the transparency change rate set by said change rate setting section, such that said writing threshold is changed in the same way as said transparency change rate, and the relationship in size between said writing threshold and the calculated transparency of each pixel remains constant, when said transparency change rate is changed.