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. <EOS>