A bicycle transmission control device is basically provided with a transmission controller that is programmed to switch between a first control state and a second control state. The bicycle transmission control device operates in accordance with the first control state for controlling a transmission based on a first signal that is input from a first detector, which detects a rotation of a crank. The bicycle transmission control device operates in accordance with the second control state for controlling the transmission based on a second signal that is input from a second detector, which detects a value reflecting a bicycle speed.