An insertion system includes an enclosure supply device, an envelope supply device, an insertion device to insert an enclosure supplied from the enclosure supply device into the envelope supplied from the envelope supply device, a first input unit to input identification data of the enclosure inserted into the envelope in each of multiple insertion setting records, a second input unit to input identification data of the enclosure set in the enclosure container of the enclosure supply device, and a controller to determine whether the identification data of the enclosure to be inserted, input by the first input unit, matches the identification data of the enclosure set in the enclosure container, input by the second input unit, and to control supply of the envelope by the envelope supply device as well as supply of the enclosure by the enclosure supply device based on a result of the determination.