A video slot machine starts spinning display of video reels upon detecting a spin operation, and performs a lottery to determine a special position in symbol stop positions in a reel display area. A character appears behind the video reel in such a manner that a displayed range of the character includes the symbol stop position determined to be the special position. When the video reels stop with a chance symbol stopped in front of the character, a replacement target is selected from the change symbol and other symbols in its periphery in accordance with a section of the character stopped by the chance symbol. Then, outcome of the reels is determined with the replacement target symbols replaced with a reward symbol, and payout is performed.