A radio communication terminal apparatus configured to communicate with a base station in a communication system in which a plurality of reference signals of a plurality of sequence groups are beforehand determined in association with a plurality of sequence group numbers, the sequence group numbers each having an offset added thereto are allocated to cells, the offset temporally varies depending on a hopping pattern that is common in one cell cluster and that is different among a plurality of cell clusters, and the offset is different from those of other cells belonging to the same cell cluster, the apparatus comprising: a control section that is adapted to determine a sequence group number for generating a demodulation reference signal, DMRS; a reference signal generation section that is adapted to generate a DMRS of a sequence group corresponding to the determined sequence group number; and a radio transmission section that is adapted to transmit the generated DMRS, wherein: the sequence group number is determined by adding a variable offset, that varies depending on time when an instruction to use a sequence group which is different from a cell-specific sequence group specifically signaled for the radio communication terminal apparatus by Radio Resource Control, RRC, layer information is received, the cell-specific sequence group being a sequence group allocated to a cell which contains the radio communication terminal apparatus, and the sequence group number is represented by an integer modulo N SG, the variable offset satisfies the relationship of the following expressions to: F n s mod N SG ≠ 0 Pr F n s = x ≤ 3 / X X ≥ 0.5 × N TS where n s is a time slot; N SG is the number of the plurality of sequence groups, or the number of cells belonging to one cell cluster; F(n s) is the value of the variable offset in the time slot n s; X is the element number of a set of all the values taken in reality as a value x of the variable offset and satisfying the expressions and; and N TS is the number of time slots for one cycle period of cyclically repeating allocation of the sequence group number; and the variable offset F(n s) is represented by the following expression: F n s = λ × n s + z where λ and z are integers other than zero and satisfying the expressions to. a control section that is adapted to determine a sequence group number for generating a demodulation reference signal, DMRS; a reference signal generation section that is adapted to generate a DMRS of a sequence group corresponding to the determined sequence group number; and a radio transmission section that is adapted to transmit the generated DMRS, wherein: the sequence group number is determined by adding a variable offset, that varies depending on time when an instruction to use a sequence group which is different from a cell-specific sequence group specifically signaled for the radio communication terminal apparatus by Radio Resource Control, RRC, layer information is received, the cell-specific sequence group being a sequence group allocated to a cell which contains the radio communication terminal apparatus, and the sequence group number is represented by an integer modulo N SG, the variable offset satisfies the relationship of the following expressions to: F n s mod N SG ≠ 0 Pr F n s = x ≤ 3 / X X ≥ 0.5 × N TS where n s is a time slot; N SG is the number of the plurality of sequence groups, or the number of cells belonging to one cell cluster; F(n s) is the value of the variable offset in the time slot n s; X is the element number of a set of all the values taken in reality as a value x of the variable offset and satisfying the expressions and; and N TS is the number of time slots for one cycle period of cyclically repeating allocation of the sequence group number; and the variable offset F(n s) is represented by the following expression: F n s = λ × n s + z where λ and z are integers other than zero and satisfying the expressions to. the sequence group number is determined by adding a variable offset, that varies depending on time when an instruction to use a sequence group which is different from a cell-specific sequence group specifically signaled for the radio communication terminal apparatus by Radio Resource Control, RRC, layer information is received, the cell-specific sequence group being a sequence group allocated to a cell which contains the radio communication terminal apparatus, and the sequence group number is represented by an integer modulo N SG, the variable offset satisfies the relationship of the following expressions to: F n s mod N SG ≠ 0 Pr F n s = x ≤ 3 / X X ≥ 0.5 × N TS where n s is a time slot; N SG is the number of the plurality of sequence groups, or the number of cells belonging to one cell cluster; F(n s) is the value of the variable offset in the time slot n s; X is the element number of a set of all the values taken in reality as a value x of the variable offset and satisfying the expressions and; and N TS is the number of time slots for one cycle period of cyclically repeating allocation of the sequence group number; and where n s is a time slot; N SG is the number of the plurality of sequence groups, or the number of cells belonging to one cell cluster; F(n s) is the value of the variable offset in the time slot n s; X is the element number of a set of all the values taken in reality as a value x of the variable offset and satisfying the expressions and; and N TS is the number of time slots for one cycle period of cyclically repeating allocation of the sequence group number; and the variable offset F(n s) is represented by the following expression: F n s = λ × n s + z