An insertion system includes an insertion apparatus including an insertion section, a fiber sensor configured to detect a bend shape of the insertion section, an attitude detector, and an attitude shape calculator. The attitude detector is configured to detect at least one of a first rotational change quantity related to a change quantity of rotation about a longitudinal direction of the insertion apparatus, and a first directional change quantity related to a change quantity of the longitudinal direction. The attitude shape calculator is configured to calculate attitude shape information including at least one of a change quantity of rotation of the bend shape and a change quantity of a direction of the bend shape, based on the bend shape and the at least one of the first rotational change quantity and first directional change quantity.
