A smoking system comprising: a secondary device which comprises a load for atomizing an aerosol source or heating a flavor source, and a power source which can supply electric power to the load; a primary device which can supply, when it is connected to the secondary device, electric power to the load and the power source; and a control part which can execute a first mode for supplying electric power from the primary device to the load and a second mode for supplying electric power from the primary device to the power source; characterised in that in changing between the first mode and the second mode, in at least one of a first transition direction from the first mode to the second mode, and a second transition direction from the second mode to the first mode, the control part executes a transition mode lasting for a transition time during which a predetermined variable relating to supply of electric power is changed, wherein the predetermined variable is a quantity of electric power supplied from the primary device to the secondary device; and the control part executes the respective modes in such a manner that: a first quantity of electric power is supplied from the primary device to the load in the first mode; a process for reducing the quantity of to-be-supplied electric power from the first quantity is applied to the primary device, and supply of electric power from the primary device to the power source is not performed, in the transition mode in the first transition direction; and a second quantity, that is smaller than the first quantity, of electric power is supplied from the primary device to the power source in the second mode. a secondary device which comprises a load for atomizing an aerosol source or heating a flavor source, and a power source which can supply electric power to the load; a primary device which can supply, when it is connected to the secondary device, electric power to the load and the power source; and a control part which can execute a first mode for supplying electric power from the primary device to the load and a second mode for supplying electric power from the primary device to the power source; characterised in that in changing between the first mode and the second mode, in at least one of a first transition direction from the first mode to the second mode, and a second transition direction from the second mode to the first mode, the control part executes a transition mode lasting for a transition time during which a predetermined variable relating to supply of electric power is changed, wherein the predetermined variable is a quantity of electric power supplied from the primary device to the secondary device; and the control part executes the respective modes in such a manner that: a first quantity of electric power is supplied from the primary device to the load in the first mode; a process for reducing the quantity of to-be-supplied electric power from the first quantity is applied to the primary device, and supply of electric power from the primary device to the power source is not performed, in the transition mode in the first transition direction; and a second quantity, that is smaller than the first quantity, of electric power is supplied from the primary device to the power source in the second mode. a first quantity of electric power is supplied from the primary device to the load in the first mode; a process for reducing the quantity of to-be-supplied electric power from the first quantity is applied to the primary device, and supply of electric power from the primary device to the power source is not performed, in the transition mode in the first transition direction; and a second quantity, that is smaller than the first quantity, of electric power is supplied from the primary device to the power source in the second mode.