an electronic instrument includes a connection detector detecting whether a connector is connected with an external storage unit , an operation unit , operated by an operator , outputting an operating signal having one of first and second states in accordance with an operation of the operator , a boot selection controller selecting a device to be booted from a nonvolatile rewritable memory and the external storage unit in accordance with a detection result of the connection detector and a state of the operation signal from the operation unit , and a determination unit whether the external storage unit stores a program when the external unit is selected as the device to be booted . the boot selection controller includes a first control unit selecting the external storage unit as the device to be booted when the external storage unit is connected to the connector and the operation unit outputs the operating signal having the first state ; and a second control unit changing the device to be booted from the external storage unit to the nonvolatile rewritable memory when the determining unit determines that the external storage unit does not stores the program and the operation unit outputs the operating signal having the second state .