A start control device for an outboard motor performing a control to start and stop the outboard motor in accordance with an instruction made by a boat operator, the start control device for the outboard motor comprising: an authentication means performing an authentication of a portable machine carried by the boat operator via a communication part in accordance with an operation of a start switch made by the boat operator; an electric power supply instruction means instructing a supply of electric power to the outboard motor based on a success of the authentication of the portable machine performed by the authentication means; characterized in that a security cancellation instruction means instructing a cancellation of security of the outboard motor based on the success of the authentication of the portable machine performed by the authentication means; a rotation speed determination means determining whether or not a rotation speed of an engine of the outboard motor is 0 (zero), when the start switch is operated by the boat operator in the state where the electric power is supplied to the outboard motor in accordance with the instruction made by the electric power supply instruction means, and the security of the outboard motor is cancelled in accordance with the instruction made by the security cancellation instruction means; a determination means determining whether or not an emergency switch is on when the rotation speed determination means determines that the rotation speed is 0 (zero); a start instruction means instructing a start of the engine of the outboard motor when the rotation speed determination means determines that the rotation speed of the engine is 0 (zero), and when the determination means determines that the emergency switch is not on; and a stop instruction means instructing a stop of the engine of the outboard motor when the rotation speed determination means determines that the rotation speed is not 0 (zero), or instructing a stop of the supply of electric power to the outboard motor when the rotation speed determination means determines that the rotation speed of the engine is 0 (zero), and when the determination means determines that the emergency switch is on. an authentication means performing an authentication of a portable machine carried by the boat operator via a communication part in accordance with an operation of a start switch made by the boat operator; an electric power supply instruction means instructing a supply of electric power to the outboard motor based on a success of the authentication of the portable machine performed by the authentication means; characterized in that a security cancellation instruction means instructing a cancellation of security of the outboard motor based on the success of the authentication of the portable machine performed by the authentication means; a rotation speed determination means determining whether or not a rotation speed of an engine of the outboard motor is 0 (zero), when the start switch is operated by the boat operator in the state where the electric power is supplied to the outboard motor in accordance with the instruction made by the electric power supply instruction means, and the security of the outboard motor is cancelled in accordance with the instruction made by the security cancellation instruction means; a determination means determining whether or not an emergency switch is on when the rotation speed determination means determines that the rotation speed is 0 (zero); a start instruction means instructing a start of the engine of the outboard motor when the rotation speed determination means determines that the rotation speed of the engine is 0 (zero), and when the determination means determines that the emergency switch is not on; and a stop instruction means instructing a stop of the engine of the outboard motor when the rotation speed determination means determines that the rotation speed is not 0 (zero), or instructing a stop of the supply of electric power to the outboard motor when the rotation speed determination means determines that the rotation speed of the engine is 0 (zero), and when the determination means determines that the emergency switch is on.