An impeller for a liquid pump comprising: a disc; i blades disposed on the disc in a circumferential direction; and i grooves provided on the disc, each of which is sandwiched between the blades, characterized in that an angle formed by a line segment connecting the center of an n-th blade to the center of the disc and a line segment connecting the center of an (n+1)-th blade, which is however the 1st blade when n=i, to the center of the disc is set as an n-th pitch angle θn of an n-th blade groove, wherein n is an integer from 1 to i; the next pitch angle to the n-th pitch angle is set as a k-th pitch angle among pitch angles having the same value as the n-th pitch angle, and an angle obtained by integrating consecutive pitch angles from the n-th pitch angle to a (k-1)-th pitch angle is set as an integrated pitch angle; and in that the following requirements are satisfied: i) the grooves are divided into a plurality of groups, each of the groups is constituted by m grooves arranged in series, with m≥5, however, in a case where i/m is not an integer, one group is constituted by the remaining number of grooves, namely 1, 2, 3 or 4 grooves; ii) in each group, the values of pitch angles are different; iii) in each group, the series of the values of pitch angles arranged in ascending order have the relationship of equal differences; iv) in each group, the minimum value of the pitch angles is set as θmin and the maximum value is set as θmax, and θmax-θmin≤5°; v) an integrated pitch angle has a single value that is different from those of the other integrated pitch angles or a value common for a pair of two integrated pitch angles is different from those of the other integrated pitch angles; and vi) the number of pairs of integrated pitch angles having common values does not exceed i×0.18. a disc; i blades disposed on the disc in a circumferential direction; and i grooves provided on the disc, each of which is sandwiched between the blades, characterized in that an angle formed by a line segment connecting the center of an n-th blade to the center of the disc and a line segment connecting the center of an (n+1)-th blade, which is however the 1st blade when n=i, to the center of the disc is set as an n-th pitch angle θn of an n-th blade groove, wherein n is an integer from 1 to i; the next pitch angle to the n-th pitch angle is set as a k-th pitch angle among pitch angles having the same value as the n-th pitch angle, and an angle obtained by integrating consecutive pitch angles from the n-th pitch angle to a (k-1)-th pitch angle is set as an integrated pitch angle; and in that the following requirements are satisfied: i) the grooves are divided into a plurality of groups, each of the groups is constituted by m grooves arranged in series, with m≥5, however, in a case where i/m is not an integer, one group is constituted by the remaining number of grooves, namely 1, 2, 3 or 4 grooves; ii) in each group, the values of pitch angles are different; iii) in each group, the series of the values of pitch angles arranged in ascending order have the relationship of equal differences; iv) in each group, the minimum value of the pitch angles is set as θmin and the maximum value is set as θmax, and θmax-θmin≤5°; v) an integrated pitch angle has a single value that is different from those of the other integrated pitch angles or a value common for a pair of two integrated pitch angles is different from those of the other integrated pitch angles; and vi) the number of pairs of integrated pitch angles having common values does not exceed i×0.18. i) the grooves are divided into a plurality of groups, each of the groups is constituted by m grooves arranged in series, with m≥5, however, in a case where i/m is not an integer, one group is constituted by the remaining number of grooves, namely 1, 2, 3 or 4 grooves; ii) in each group, the values of pitch angles are different; iii) in each group, the series of the values of pitch angles arranged in ascending order have the relationship of equal differences; iv) in each group, the minimum value of the pitch angles is set as θmin and the maximum value is set as θmax, and θmax-θmin≤5°; v) an integrated pitch angle has a single value that is different from those of the other integrated pitch angles or a value common for a pair of two integrated pitch angles is different from those of the other integrated pitch angles; and vi) the number of pairs of integrated pitch angles having common values does not exceed i×0.18.