An electrically power assisted bicycle, comprising: a driving system including an electric motor configured to generate an assist force assisting human power of a rider and including a control unit configured to control an operation of the electric motor; and an operation panel including a plurality of buttons (64a,64b,66,68,70) and a control circuit; wherein: the plurality of buttons (64a,64b,66,68,70) include a power button configured to turn on or off a power of the driving system, and an assist force setting button (64a,64b) configured to set an assist force of the electric motor; the control circuit is configured to accept a press on each of the plurality of buttons (64a,64b,66,68,70) to execute a predefined process; characterized in that when the control circuit accepts a second operation different from a first operation on at least one button among the plurality of buttons (64a,64b,66,68,70) while electric power is supplied to the driving system and the control circuit is configured to be operated in a first operation mode, the control circuit is configured to prohibit the power from being turned off, wherein the control circuit is operable in one of the first operation mode and a power lock mode; in the first operation mode, each time the power button is pressed, the power is turned on and off alternately; in the power lock mode, the power is prohibited from being turned off when the first operation is made on the power button; and when accepting the second operation on the at least one button in the first operation mode, the control circuit is configured to change from the first operation mode to the power lock mode. a driving system including an electric motor configured to generate an assist force assisting human power of a rider and including a control unit configured to control an operation of the electric motor; and an operation panel including a plurality of buttons (64a,64b,66,68,70) and a control circuit; wherein: the plurality of buttons (64a,64b,66,68,70) include a power button configured to turn on or off a power of the driving system, and an assist force setting button (64a,64b) configured to set an assist force of the electric motor; the control circuit is configured to accept a press on each of the plurality of buttons (64a,64b,66,68,70) to execute a predefined process; characterized in that when the control circuit accepts a second operation different from a first operation on at least one button among the plurality of buttons (64a,64b,66,68,70) while electric power is supplied to the driving system and the control circuit is configured to be operated in a first operation mode, the control circuit is configured to prohibit the power from being turned off, wherein the control circuit is operable in one of the first operation mode and a power lock mode; in the first operation mode, each time the power button is pressed, the power is turned on and off alternately; in the power lock mode, the power is prohibited from being turned off when the first operation is made on the power button; and when accepting the second operation on the at least one button in the first operation mode, the control circuit is configured to change from the first operation mode to the power lock mode. the plurality of buttons (64a,64b,66,68,70) include a power button configured to turn on or off a power of the driving system, and an assist force setting button (64a,64b) configured to set an assist force of the electric motor; the control circuit is configured to accept a press on each of the plurality of buttons (64a,64b,66,68,70) to execute a predefined process; characterized in that when the control circuit accepts a second operation different from a first operation on at least one button among the plurality of buttons (64a,64b,66,68,70) while electric power is supplied to the driving system and the control circuit is configured to be operated in a first operation mode, the control circuit is configured to prohibit the power from being turned off, wherein the control circuit is operable in one of the first operation mode and a power lock mode; in the first operation mode, each time the power button is pressed, the power is turned on and off alternately; in the power lock mode, the power is prohibited from being turned off when the first operation is made on the power button; and when accepting the second operation on the at least one button in the first operation mode, the control circuit is configured to change from the first operation mode to the power lock mode.