A life prediction method for an optical module, the optical module being configured to keep optical output constant by controlling a bias current that is applied to a laser diode, the method comprising the following method steps, which are carried out by a life prediction device (1; 1a; 1b): a first step of acquiring, by a bias current acquisition unit of the life prediction device (1; 1a; 1b) and from the optical module, a bias current value that is a current value of the bias current; a second step of holding, by an initial value holding unit of the life prediction device (1; 1a; 1b), an initial bias current value that is an initial current value of the bias current; a third step of calculating, by a monitoring unit (13; 13b) of the life prediction device (1; 1a; 1b), a number of digits of a difference value between the bias current value and the initial bias current value, and determining whether there is an increase in the number of digits; a fourth step of calculating, by a time interval calculation unit (14; 14a; 14b) of the life prediction device (1; 1a; 1b), a time interval at which occurrence of the increase in the number of digits is detected; and a fifth step of estimating, by a life calculation unit (15; 18; 16b) of the life prediction device (1; 1a; 1b), a life of the optical module using the time interval, a first threshold and the number of digits; wherein the life is a remaining life of the optical module, and wherein the life calculation unit (15; 18; 16b) calculates the remaining life of the optical module according to TL = Dlimit − Di * Δ T; or wherein the life is an estimated deterioration time of the optical module, and wherein the life calculation unit (15; 18; 16b) calculates the estimated deterioration time of the optical module according to TT = t + Dlimit − Di * Δ T; where TL denotes the remaining life of the optical module, TT denotes the estimated deterioration time of the optical module, Dlimit denotes the first threshold and is the number of digits of the difference value of the initial bias current value and a bias current threshold for which it is determined that the optical module has deteriorated, Di denotes the number of digits of the difference value between the i-th bias current value acquired and the initial bias current value, where i is an integer equal to two or more, ΔT denotes the time interval, and t denotes a time of the calculation of the life. a first step of acquiring, by a bias current acquisition unit of the life prediction device (1; 1a; 1b) and from the optical module, a bias current value that is a current value of the bias current; a second step of holding, by an initial value holding unit of the life prediction device (1; 1a; 1b), an initial bias current value that is an initial current value of the bias current; a third step of calculating, by a monitoring unit (13; 13b) of the life prediction device (1; 1a; 1b), a number of digits of a difference value between the bias current value and the initial bias current value, and determining whether there is an increase in the number of digits; a fourth step of calculating, by a time interval calculation unit (14; 14a; 14b) of the life prediction device (1; 1a; 1b), a time interval at which occurrence of the increase in the number of digits is detected; and a fifth step of estimating, by a life calculation unit (15; 18; 16b) of the life prediction device (1; 1a; 1b), a life of the optical module using the time interval, a first threshold and the number of digits; wherein the life is a remaining life of the optical module, and wherein the life calculation unit (15; 18; 16b) calculates the remaining life of the optical module according to TL = Dlimit − Di * Δ T; or wherein the life is an estimated deterioration time of the optical module, and wherein the life calculation unit (15; 18; 16b) calculates the estimated deterioration time of the optical module according to TT = t + Dlimit − Di * Δ T; where TL denotes the remaining life of the optical module, TT denotes the estimated deterioration time of the optical module, Dlimit denotes the first threshold and is the number of digits of the difference value of the initial bias current value and a bias current threshold for which it is determined that the optical module has deteriorated, Di denotes the number of digits of the difference value between the i-th bias current value acquired and the initial bias current value, where i is an integer equal to two or more, ΔT denotes the time interval, and t denotes a time of the calculation of the life.