A semiconductor light emitting element assembly comprising: a semiconductor laser element having a laminated structure formed by laminating a first compound semiconductor layer, an active layer, and a second compound semiconductor layer; wherein a heat sink and a sub-mount are provided, wherein the heat sink, the sub-mount, and the semiconductor laser element are sequentially laminated, and in that a Peltier element is provided being configured for heating the heat sink and thereby heating the active layer so that the temperature T act of the active layer during light emission is higher than 50 °C and smaller than 70 °C and the semiconductor laser element satisfies: ΔI 2 > ΔI 1 where ΔI 1 is an operating current range of currents for operating the semiconductor laser element at which stable laser oscillation of the semiconductor laser element occurs when the temperature T act of the active layer is T 1, and ΔI 2 is the operating current range of operating currents for operating the semiconductor laser element at which stable laser oscillation of the semiconductor laser element occurs when the temperature T act of the active layer is T 2 where T 2 > T 1, or P 2 > P 1 where P 1 is a maximum optical output emitted when the temperature T act of the active layer is T 1, and P 2 is the maximum optical output emitted when the temperature T act of the active layer is T 2 where T 2 > T 1; and I max − 2 > I max − 1 where I max-1 is an upper limit value of the operating current range ΔI 1 when the temperature T act of the active layer is T 1, and I max-2 is the upper limit value of the operating current range ΔI 2 when the temperature T act of the active layer is T 2. a semiconductor laser element having a laminated structure formed by laminating a first compound semiconductor layer, an active layer, and a second compound semiconductor layer; wherein a heat sink and a sub-mount are provided, wherein the heat sink, the sub-mount, and the semiconductor laser element are sequentially laminated, and in that a Peltier element is provided being configured for heating the heat sink and thereby heating the active layer so that the temperature T act of the active layer during light emission is higher than 50 °C and smaller than 70 °C and the semiconductor laser element satisfies: ΔI 2 > ΔI 1 where ΔI 1 is an operating current range of currents for operating the semiconductor laser element at which stable laser oscillation of the semiconductor laser element occurs when the temperature T act of the active layer is T 1, and ΔI 2 is the operating current range of operating currents for operating the semiconductor laser element at which stable laser oscillation of the semiconductor laser element occurs when the temperature T act of the active layer is T 2 where T 2 > T 1, or P 2 > P 1 where P 1 is a maximum optical output emitted when the temperature T act of the active layer is T 1, and P 2 is the maximum optical output emitted when the temperature T act of the active layer is T 2 where T 2 > T 1; and I max − 2 > I max − 1 where I max-1 is an upper limit value of the operating current range ΔI 1 when the temperature T act of the active layer is T 1, and I max-2 is the upper limit value of the operating current range ΔI 2 when the temperature T act of the active layer is T 2.