According to an embodiment, a data management apparatus includes a first receiver, a generator, a second receiver, a convertor, and a transmitter. The first receiver is configured to receive first values from at least one power meter, the first values being acquired by encrypting power usage amounts collected by the at least one power meter using the corresponding first secret key. The generator is configured to generate a second value by summing the first values. The second receiver is configured to receive a conversion key from a key management server. The conversion key is generated by using the first secret key and the second secret key. The convertor is configured to convert the second value into a third value by using the conversion key. The transmitter is configured to transmit the third value to an application server.