A biological signal drawing apparatus, drawing biological signals as drawing points in time series, the biological signal drawing apparatus comprising: a waveform image data producing unit configured to set an axis of a value of a biological signal in a vertical direction, to arrange pixel zones in a lateral direction and to set the same as a time axis, and to repeat, in the time axis direction, a process of allocating respective first numbers of sampled biological signals to the pixel zones and setting the value of each biological signal as a drawing point in each of the pixel zones; a thinner configured to perform a thinning process to thin the first number of the drawing points corresponding to the biological signals sampled in each pixel zone, to obtain a second number of the drawing points for each pixel zone, the second number being smaller than the first number; a calculator configured to calculate, after the thinning process is performed, a parameter based on at least one difference of values of adjacent two of the drawing points included in a group that includes: a first drawing point which is a center in time series in the group and which has a first value; and at least one second drawing point which precedes or succeeds the first drawing point in time series and which has a second value; and a processor configured to perform a process of: performing a weighted moving average calculation using the first value, the second value and the calculated parameter, to obtain a third value; and replacing the first value of the first drawing point with the third value. a waveform image data producing unit configured to set an axis of a value of a biological signal in a vertical direction, to arrange pixel zones in a lateral direction and to set the same as a time axis, and to repeat, in the time axis direction, a process of allocating respective first numbers of sampled biological signals to the pixel zones and setting the value of each biological signal as a drawing point in each of the pixel zones; a thinner configured to perform a thinning process to thin the first number of the drawing points corresponding to the biological signals sampled in each pixel zone, to obtain a second number of the drawing points for each pixel zone, the second number being smaller than the first number; a calculator configured to calculate, after the thinning process is performed, a parameter based on at least one difference of values of adjacent two of the drawing points included in a group that includes: a first drawing point which is a center in time series in the group and which has a first value; and at least one second drawing point which precedes or succeeds the first drawing point in time series and which has a second value; and a first drawing point which is a center in time series in the group and which has a first value; and at least one second drawing point which precedes or succeeds the first drawing point in time series and which has a second value; and a processor configured to perform a process of: performing a weighted moving average calculation using the first value, the second value and the calculated parameter, to obtain a third value; and replacing the first value of the first drawing point with the third value. performing a weighted moving average calculation using the first value, the second value and the calculated parameter, to obtain a third value; and replacing the first value of the first drawing point with the third value.