A pulse wave measuring device checks whether amplitude of a pulse signal satisfies a gain changing condition and, when the gain changing condition is satisfied, changes a gain. The pulse wave measuring device includes an amplitude storing unit and a mode progressing unit. The amplitude storing unit stores plural gain changing conditions, to which a series of order are assigned, respectively. A mode progressing unit 15 changes the gain changing condition to the next-ordered gain changing condition upon determination that the mode progress condition is satisfied. The gain changing condition is satisfied in case that Y1 or more number of pieces of X1 amplitudes are larger than an upper limit value U1 or smaller than a lower limit value L1. X1 is increased as the order of the set gain changing condition is higher.