NOVELTY - An addition hardening-type silicone composition comprises organo polysiloxane (A) having silicon atomic-union aliphatic unsaturated group, organosilicon compound (B) having hydrogen atom bonded with silicon atom, and platinum group metal-type hydrosilylation catalyst. The sum of number-of-moles (T-1) of aliphatic unsaturated group in molecular chain non-terminal portion and number-of-moles (T-2) of aliphatic unsaturated group in molecular chain terminal portion of all aliphatic unsaturated group-containing compound contained in composition in composition is 0-0.7.    USE - Addition hardening-type silicone composition is used for cured material for optical element sealing material (both claimed). Uses include but are not limited to light emitting diode, semiconductor laser, photodiode, photo-transistor, solar cell, charge coupling device.    ADVANTAGE - The addition hardening-type silicone composition provides cured material having excellent heat-resistant color-change property and transparency.    DETAILED DESCRIPTION - An addition hardening-type silicone composition comprises organo polysiloxane (A) having two or more silicon atomic union aliphatic unsaturated group per molecule, organosilicon compound (B) having hydrogen atom bonded with two or more silicon atom per molecule, and platinum group metal-type hydrosilylation catalyst. The sum of number-of-moles (T-1) of aliphatic unsaturated group in molecular chain non-terminal portion of all aliphatic unsaturated group-containing compound contained in composition, and number-of-moles (T-2) of aliphatic unsaturated group in molecular chain terminal portion of all aliphatic unsaturated group-containing compound contained in composition is 0-0.7. The ratio of number-of-moles (B) of hydrogen atom bonded with silicon atom contained in component (B) with respect to sum of (T-1) and (T-2) is 0.5-1. An INDEPENDENT CLAIM is included for cured material, which is obtained by hardening the addition hardening-type silicone composition.