A sound signal hybrid encoder comprising: a signal analysis unit configured to analyze characteristics of a sound signal to determine a scheme for encoding a frame included in the sound signal; a lapped frequency domain encoder which encodes a frame included in the sound signal by performing an LFD transform on the frame, to generate an LFD frame; a linear prediction encoder which encodes a frame included in the sound signal by calculating and using linear prediction coefficients of the frame, to generate an LP frame; a switching unit configured to switch, for frame encoding, between the LFD encoder and the LP encoder, according to a result of the determination by the signal analysis unit; a local decoder which generates a locally-decoded signal including a signal obtained by decoding at least a part of an aliasing cancellation target frame that is the LFD frame adjacent to the LP frame according to switching control by the switching unit and a signal obtained by decoding at least a part of the LP frame adjacent to the AC target frame; an AC signal generation unit configured to generate, using the sound signal and the locally-decoded signal, an AC signal used for cancelling aliasing caused when the AC target frame is decoded, and output the generated AC signal; and a quantizer which quantizes the AC signal, characterized in that, when the AC target frame is immediately after the LP frame or when the AC target frame is immediately before the LP frame, the AC signal generation unit is configured to generate an AC signal according to each of a first scheme and a second scheme that is different from the first scheme and output the AC signal, out of the two generated AC signals, that is smaller in an amount of coded data obtained by a quantization by the quantizer and output an AC flag indicating the scheme used for generating the outputted AC signal, and when the AC target frame is immediately after the LP frame, the first scheme generates the AC signal using a zero input response obtained by performing windowing on the LP frame immediately preceding the AC target frame, and the second scheme generates the AC signal without using the zero input response. a signal analysis unit configured to analyze characteristics of a sound signal to determine a scheme for encoding a frame included in the sound signal; a lapped frequency domain encoder which encodes a frame included in the sound signal by performing an LFD transform on the frame, to generate an LFD frame; a linear prediction encoder which encodes a frame included in the sound signal by calculating and using linear prediction coefficients of the frame, to generate an LP frame; a switching unit configured to switch, for frame encoding, between the LFD encoder and the LP encoder, according to a result of the determination by the signal analysis unit; a local decoder which generates a locally-decoded signal including a signal obtained by decoding at least a part of an aliasing cancellation target frame that is the LFD frame adjacent to the LP frame according to switching control by the switching unit and a signal obtained by decoding at least a part of the LP frame adjacent to the AC target frame; an AC signal generation unit configured to generate, using the sound signal and the locally-decoded signal, an AC signal used for cancelling aliasing caused when the AC target frame is decoded, and output the generated AC signal; and a quantizer which quantizes the AC signal, characterized in that, when the AC target frame is immediately after the LP frame or when the AC target frame is immediately before the LP frame, the AC signal generation unit is configured to generate an AC signal according to each of a first scheme and a second scheme that is different from the first scheme and output the AC signal, out of the two generated AC signals, that is smaller in an amount of coded data obtained by a quantization by the quantizer and output an AC flag indicating the scheme used for generating the outputted AC signal, and when the AC target frame is immediately after the LP frame, the first scheme generates the AC signal using a zero input response obtained by performing windowing on the LP frame immediately preceding the AC target frame, and the second scheme generates the AC signal without using the zero input response.