A silicone composition comprising the following components to: an organopolysiloxane having at least two alkenyl groups each bonded to a silicon atom in a molecule, having a viscosity (measured by a rotary viscometer) at 25 degrees C in the range of from 50 mPa·s to 10,000 mPa·s, and having no aryl nor aralkyl group bonded to a silicon atom, wherein a percentage of the number of the alkenyl groups relative to the number of groups each bonded to a silicon atom is from 0.01% to less than 4.5%; a mixture comprising the following components, and: an alpha-olefin which is liquid at 25 degrees C, in an amount of 0.05 to 15 parts by mass, relative to 100 parts by mass of component, an organohydrogenpolysiloxane having at least three hydrogen atoms each bonded to a silicon atom in a molecule, and having no aryl nor aralkyl group bonded to a silicon atom, wherein a ratio of the number of the SiH groups present in component to a total number of the alkenyl groups present in components and is 0.5 to 10; an organohydrogenpolysiloxane having at least three hydrogen atoms each bonded to a silicon atom in a molecule, and having an aryl group and/or an aralkyl group each bonded to a silicon atom such that a percentage of the number of the aryl group and the aralkyl group relative to a total number of hydrogen atoms and groups each bonded to a silicon atom is 8% to 50%, wherein the amount of component is from 0.05 to 10 parts by mass, relative to 100 parts by mass of component, and a ratio of the number of the SiH groups present in component to a total number of the alkenyl groups present in components and is 0.1 to 2; and a catalytic amount of a platinum group metal catalyst. an organopolysiloxane having at least two alkenyl groups each bonded to a silicon atom in a molecule, having a viscosity (measured by a rotary viscometer) at 25 degrees C in the range of from 50 mPa·s to 10,000 mPa·s, and having no aryl nor aralkyl group bonded to a silicon atom, wherein a percentage of the number of the alkenyl groups relative to the number of groups each bonded to a silicon atom is from 0.01% to less than 4.5%; a mixture comprising the following components, and: an alpha-olefin which is liquid at 25 degrees C, in an amount of 0.05 to 15 parts by mass, relative to 100 parts by mass of component, an organohydrogenpolysiloxane having at least three hydrogen atoms each bonded to a silicon atom in a molecule, and having no aryl nor aralkyl group bonded to a silicon atom, wherein a ratio of the number of the SiH groups present in component to a total number of the alkenyl groups present in components and is 0.5 to 10; an organohydrogenpolysiloxane having at least three hydrogen atoms each bonded to a silicon atom in a molecule, and having an aryl group and/or an aralkyl group each bonded to a silicon atom such that a percentage of the number of the aryl group and the aralkyl group relative to a total number of hydrogen atoms and groups each bonded to a silicon atom is 8% to 50%, wherein the amount of component is from 0.05 to 10 parts by mass, relative to 100 parts by mass of component, and a ratio of the number of the SiH groups present in component to a total number of the alkenyl groups present in components and is 0.1 to 2; and an alpha-olefin which is liquid at 25 degrees C, in an amount of 0.05 to 15 parts by mass, relative to 100 parts by mass of component, an organohydrogenpolysiloxane having at least three hydrogen atoms each bonded to a silicon atom in a molecule, and having no aryl nor aralkyl group bonded to a silicon atom, wherein a ratio of the number of the SiH groups present in component to a total number of the alkenyl groups present in components and is 0.5 to 10; an organohydrogenpolysiloxane having at least three hydrogen atoms each bonded to a silicon atom in a molecule, and having an aryl group and/or an aralkyl group each bonded to a silicon atom such that a percentage of the number of the aryl group and the aralkyl group relative to a total number of hydrogen atoms and groups each bonded to a silicon atom is 8% to 50%, wherein the amount of component is from 0.05 to 10 parts by mass, relative to 100 parts by mass of component, and a ratio of the number of the SiH groups present in component to a total number of the alkenyl groups present in components and is 0.1 to 2; and a catalytic amount of a platinum group metal catalyst.