A controller characterized with a function for adjusting the controller to provide an optimal operational feel to a player comprises a main body configured to be held by the player performing a game, a plurality of operational keys arranged on the main body, a pair of analog stick means arranged on the main body, a switch arranged in contact with the plurality of operational keys and a plurality of adjustment parts for adjusting key stroke of the plurality of operational keys. The plurality of operational keys is configured to be operated by a finger of the player. The plurality of plurality of operational keys, the switch and the plurality of adjustment parts are configured to be adjusted by the player holding the controller so as to achieve an optimal operational feel, according to the player's preferences and game characteristics.