1. An image decoding method for decoding coded image data on a block-by-block basis, the image decoding method comprising: segmenting a block including a current signal to be decoded that is part of the coded image data, into a first plurality of groups, a second plurality of groups, and a third plurality of groups according to a type of the current signal, wherein each of the groups in the first plurality of groups, each of the groups in the second plurality of groups, and each of the groups in the third plurality of groups corresponds to a different frequency component range; determining a context corresponding to each of the groups in the first plurality of groups to generate a first set of mapping information, determining a context corresponding to each of the groups in the second plurality of groups to generate a second set of mapping information, and determining a context corresponding to each of the groups in the third plurality of groups to generate a third set of mapping information, wherein the first set of mapping information indicates a correspondence between each of the groups in the first plurality of groups and a corresponding context, the second set of mapping information indicates a correspondence between each of the groups in the second plurality of groups and a corresponding context, and the third set of mapping information indicates a correspondence between each of the groups in the third plurality of groups and a corresponding context; receiving, from the coded image data, an identifier which identifies one of (i) the first set of mapping information, (ii) the second set of mapping information, or (iii) the third set of mapping information; performing binary arithmetic decoding on the current signal according to a probability information item corresponding to a context indicated by the received identifier, to generate binarized coefficients, the context corresponding to the group having the current signal; and updating, for each of probability information items, the probability information item corresponding to the context, based on the coefficient included in the group corresponding to the context, wherein in the segmenting, the block is segmented into the first plurality of groups, the second plurality of groups, and the third plurality of groups such that the number of the groups in each of the first plurality of groups, the second plurality of groups, and the third plurality of groups is respectively different.