To provide an average specific filtration resistance calculator for rapidly calculating average specific filtration resistance αav, and also to provide its program.

In this average specific filtration resistance calculator 1 for a solid particle layer acquired by filtering slurry at an arbitrary ΔP, input data (t, αpt) from an input means 2 are fitted to an equation, αpt=Aln(t)+B, by a first fitting means 4 to determine parameters A and B of each compression pressure Ps. An αp determining means 6 determines αpt causing the equation, into which A and B are substituted, to give an increment Δαpt of αpt corresponding to an increment Δt of t equal to or less than a prescribed value, determining the αpt as specific filtration resistance αp. A second fitting means 8 determines α0 and n by fitting αp data (Ps, αp) to an equation, αp=α0×Psn. An average specific filtration resistance determining means 10 determines average specific filtration resistance αav from α0 and n by using an equation, αav=α0(1-n)ΔPn.