while(1)
{
  old_left_key_state = left_key_state;
  old_right_key_state = right_key_state;

  if(CheckHitKey(LEFT_KEY)){ left_key_state = PUSH; }
  else{ left_key_state = RELEASE; }
  
  if(CheckHitKey(RIGHT_KEY)){ right_key_state = PUSH; }
  else{ right_key_state = RELEASE; }

  if(left_key_state == PUSH && right_key_state == RELEASE){ press_key = LEFT_KEY; }
  if(left_key_state == RELEASE && right_key_state == PUSH) { press_key = RIGHT_KEY; }
  if(left_key_state == RELEASE && right_key_state == RELEASE){ press_key = NONE; }

  if(left_key_state == PUSH && right_key_state == PUSH){
    if(left_key_state == PUSH && old_left_key_state == RELEASE){ press_key = LEFT_KEY; }
    if(right_key_state == PUSH && old_right_key_state == RELEASE){ press_key = RIGHT_KEY; }
  }
}